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Continuous-flow rhodium-catalysed hydroformylation of long chain alkenes has been achieved with selectivities to the desired linear aldehyde of 92% and minimum rhodium loss, using a xantphos-derived ligand attached to an imidazolium salt in a supercritical fluid–ionic liquid system. The effect of oxygen in the system can be ameliorated to some extent by adding a simple sulfonated triphenylphosphine to the catalytic solution. [ABSTRACT FROM AUTHOR]

The immobilization of N-sulfonyl-(Ra)-binam-d-prolinamide using polystyrene as a support allows the recovery of an efficient catalytic system for the enantioselective direct aldol reaction between different ketones and aldehydes under solvent-free or aqueous conditions. The polystyrene-supported N-sulfonyl-(Ra)-binam-d-prolinamide catalyst in combination with benzoic acid showed similar results to those obtained with unsupported N-tosyl-binam-derived prolinamide under similar reaction conditions. The aldol products were obtained at room temperature and using only 2 equivalents of the ketone with high yields, regio-, diastereo- and enantioselectivities. The aldol reaction between aldehydes can also be performed under these reaction conditions with moderate results. The recovered catalyst can be reused up to six times without having a detrimental effect on the achieved results. [ABSTRACT FROM AUTHOR]

The first example of a chiral Lewis acid-catalyzed enantioselective hetero-Diels–Alder (HDA) reaction between 1-dimethylamino-3-silyloxy-1,3-butadiene (Rawal’s diene) and aldehydes is described. The cycloaddition reaction under the influence of 1 mol% of dirhodium(ii) tetrakis[N-benzene-fused-phthaloyl-(S)-piperidinonate], Rh2(S-BPTPI)4, proceeded cleanly and gave, after treatment with acetyl chloride, the corresponding dihydropyranones in up to 99% ee. [ABSTRACT FROM AUTHOR]

4-Substituted oxazolines, which are readily synthesized from naturally occurring α-amino acids, are converted efficiently and stereospecifically to β-amidoaldehydes in the presence of synthesis gas and catalytic dicobalt octacarbonyl. [ABSTRACT FROM AUTHOR]

New C2-symmetric tetrafluorobenzobarrelene ligands were prepared and applied successfully to the rhodium-catalyzed asymmetric addition of arylboronic acids to aromatic aldehydes giving chiral diarylmethanols in high yield with high enantioselectivity. [ABSTRACT FROM AUTHOR]

The catalytic pyrolysis of guaiacol-based lignin monomers, vanillin, syringol, and eugenol over commercial HZSM-5 has been investigated using operando Photoelectron Photoion Coincidence (PEPICO) spectroscopy to unveil the reaction mechanism by detecting reactive intermediates, such as quinone methides and ketenes, and products. Vanillin shares the decomposition mechanism with guaiacol due to prompt and efficient decarbonylation, which allows us to control this reaction leading to a phenol selectivity increase by switching to a faujasite catalyst and decreasing the Si/Al ratio. Syringol first demethylates to 3-methoxycatechol, which mainly dehydroxylates to o- and m-guaiacol. Ketene formation channels over HZSM-5 are less important here than for guaiacol or vanillin, but product distribution remains similar. C3 addition to guaiacol yields eugenol, which shows a more complex product distribution upon catalytic pyrolysis. By analogies to monomers with simplified functionalization, namely allylbenzene, 4-allylcatechol, and 4-methylcatechol, the eugenol chemistry could be fully resolved. Previously postulated reactive semi-quinone intermediates are detected spectroscopically, and their involvement opens alternative pathways to condensation and phenol formation. Allyl groups, produced by dehydroxylation of the β-O-4 bond, may not only decompose via C1/C2/C3 loss, but also cyclize to indene and its derivatives over HZSM-5. This comparably high reactivity leads to an unselective branching of the chemistry and to a complex product distribution, which is difficult to control. Indenes and naphthalenes are also prototypical coke precursors efficiently deactivating the catalyst. We rely on these mechanistic insights to discuss strategies to fine-tune process conditions to increase the selectivities of desired products by enhancing either vanillin and guaiacol or supressing eugenol yields from native lignin. [ABSTRACT FROM AUTHOR]

N-Substituted 5-(hydroxymethyl)-2-furfuryl amines have been obtained through the reductive amination of 5-hydroxymethylfurfural (HMF) with a variety of primary amines using a non-noble metal catalyst based on monodisperse Co nanoparticles covered by a thin carbon layer. The Co@C catalyst was highly active, selective and stable, allowing us to perform the reductive amination of HMF under very mild reaction conditions (60 °C and 4 bar H2) using ethanol as a green solvent and achieve the corresponding amino-alcohol in yields ranging from 80 to 99%. Moreover, the reaction was extended to other furanic aldehydes with excellent success. Furthermore, in order to synthesize amino-ester derivatives, precursors of ammonium salt-based surfactants, the reductive amination of HMF with methylamine was coupled with the selective esterification of the hydroxymethyl group of the furan ring with fatty acids using lipase CALB (Novozym 435) as a biocatalyst in 2-methyltetrahydrofuran as a green and enzyme compatible solvent, achieving practically total conversion to the corresponding amino-esters. The process was implemented in flow reactors by combining two consecutive fixed bed reactors, achieving a global yield of the amino-ester derivative of 85%, which was maintained over 86 h of operation. [ABSTRACT FROM AUTHOR]

Selective oxidation of alcohols to aldehydes/ketones is an important reaction in the fine and bulk chemicals fields. However, the classical alcohol oxidation methods are often performed under unfriendly conditions or use stoichiometric oxidants. Herein, we report an ingenious system that enables high selectivity (up to 99%) and high conversion (up to 97%) with high reaction rates in the aerobic oxidation of alcohols to aldehydes/ketones for a broad range of alcohols, proceeding smoothly via mixing the solvent ethyl acetate and HBr under ambient conditions with visible light irradiation. Experimental characterization and theoretical calculations reveal that solvated dispersion intermediates are formed spontaneously in situ through noncovalent interactions among the molecules in the reaction system, which is proposed to be the origin of the high selectivity and high activity of this reaction. The dispersion system provides a feasible activation approach for aerobic oxidation of alcohols to aldehydes/ketones with high performance under visible light. [ABSTRACT FROM AUTHOR]

The possible catalytic mechanism was proposed and studied comprehensively at the M062X/6-31G(d,p) level of theory for a reported chemoselective intermolecular SN2 nucleophilic substitution of aldehydes with alkanolamine. The calculated results show that the catalytic cycle occurs through six stages, namely, the nucleophilic attack of active N-heterocyclic carbene (NHC) on the substrate, generation of the Breslow intermediate, oxidative addition of NBS and alkanolamine, SN2 nucleophilic substitution, Et3N-assisted debromination, and finally regeneration of the NHC along with the release of the product. The results show that TSs of the C–N or C–O bond formation is the key transition state that determines the chemoselectivity of the title reaction. Moreover, our results demonstrated that the N-bromoamine intermediate is more favorable both thermodynamically and kinetically than hypobromite by 14.2 kcal mol−1, which is consistent with the fact that only the N-acylation product was observed in the experiment. In addition, we found that alkanolamine not only acts as a reactant but also as a proton-shuttle and stabilizer to stabilize the structure of the favored chemoselective transition state by multiple N–H⋯N, N–H⋯O and C–H⋯Br− noncovalent interactions. Et3N firstly acts as a base to promote the formation of the active catalyst NHC, then the protonated Et3N acts as a proton-shuttle to accelerate the Breslow intermediate formation and decrease the activation barrier. The Parr functions and frontier molecular orbital analyses of key species indicate that NHC remarkably enhances the nucleophilicity of the substrate aldehyde, leading to a significant increase of the HOMO energy and a moderate increase of the LUMO energy. We hope this work could provide deeper insights into the fundamental mechanisms of the Et3N-assisted NHC-catalyzed SN2 substitution reactions. [ABSTRACT FROM AUTHOR]

This work focuses on the development and investigation of a Rh/TPP catalytic system for the synthesis of saturated aliphatic carboxylic acids from readily available oxygenated substrates, H2 and non-toxic, renewable CO2. Optimization of the reaction conditions and reagents was carried out using 2-butanol and 1-butanol as typical secondary and primary alcohols. Afterwards, the reaction system was investigated in-depth with a separate investigation of the reverse water–gas-shift-reaction and the carbonylation reaction as key steps of the overall tandem transformation. Based on these results, a reaction network was established with two distinct main pathways. While the secondary alcohols are converted preferentially via acid catalysed dehydration to the corresponding olefins followed by hydroxycarbonylation, the primary alcohols react primarily via nucleophilic substitution to the iodide compound followed by a Monsanto-type carbonylation. Based on these results, a broad range of alcohols including bio-based substrates was converted to the corresponding C1 elongated carboxylic acids. Additionally, other oxygenated substrates such as aldehydes, ketones and industrially relevant substrate mixtures were applied successfully. [ABSTRACT FROM AUTHOR]

We demonstrate that transketolase variants from Geobacillus stearothermophilus catalyse an acyloin condensation reaction involving two hydroxylated or not aliphatic aldehydes. This promiscuous TK-catalysed reaction offers an attractive alternative to the ketol transfer from α-ketoacids used as donor substrates in the usual TK mechanism, adding atom economy by avoiding carbon dioxide release. Transketolase variants H102L/L118I/H474G(S) showed a de novo activity towards the self-condensation of propanal, and to a lesser extent of ethanal, and a remarkable ability to control the selectivity of the more challenging cross-acyloin condensation reaction with propanal or iso-butanal used as nucleophiles, and different hydroxylated aldehydes (C2–C4) as electrophiles. The synthesis of seven aliphatic symmetrical and unsymmetrical α-hydroxyketones was performed from stoichiometric amounts of aldehydes, giving yields similar to those obtained with the common TK reaction based on α-ketoacid decarboxylation. This novel enzymatic cross-acyloin condensation reaction extends the toolbox for the synthesis of unsymmetrical aliphatic α-hydroxyketones while improving mass metrics of previous enzymatic and chemical strategies. [ABSTRACT FROM AUTHOR]

Hydrazones as organometallic equivalents have emerged as a general and sustainable strategy to utilize naturally abundant aldehydes and ketones as feedstocks while only releasing water and nitrogen gas as byproducts. Yet the addition of these carbanion equivalents to carbonyl compounds has been limited to the use of precious metals as catalysts and hazardous solvents under an inert atmosphere. Herein, we report the development of a manganese-based catalyst system for the addition of aldehydes to carbonyl compounds producing secondary and tertiary alcohols with yields of up to 91%. Furthermore, this method has proven robust and reproducible under aqueous and aerobic conditions to employ an earth-abundant metal catalyst, hence advancing hydrazone umpolung chemistry to be more sustainable and operationally simple. [ABSTRACT FROM AUTHOR]

A novel photocatalytic acylation strategy was developed harnessing tetrabutylammonium decatungstate (TBADT) as a hydrogen atom transfer (HAT) photocatalyst to facilitate the direct coupling of aldehydes with N-heterocycles at ambient temperature. This approach realizes the direct acylation of N-hetrerocycles without the need for noble metals, acids, or external oxidants, thereby marking a significant advance in green chemistry protocols. Utilizing this photocatalyzed method, we successfully synthesized a diverse array of 3-acylated azauracils and quinoxalin-2(1H)-ones, adorned with a variety of functional groups, achieving yields ranging from good to excellent. This research opens avenues for the rapid and efficient modification of heterocyclic compounds, which are foundational structures in medicinal chemistry and materials science. [ABSTRACT FROM AUTHOR]

We designed a robust and efficient greener synthetic protocol to access p-quinone fused 5-substituted-1,4-benzodiazepine scaffolds, a new molecular hybrid, through InCl3 mediated Pictet–Spengler type cycloannulation of 2-amino-3-arylamino-p-quinone and commercially prevalent aldehydes. This protocol would ease access to privileged redox-active p-quinone fused seven-membered frameworks that are difficult to access by other protocols and would find potential applications in biological and electrochemical research. [ABSTRACT FROM AUTHOR]

Bicyclo[1.1.1]pentanes (BCPs), which can serve as bioisosteres of para-disubstituted benzene rings, have emerged as useful bioactive scaffolds in drug discovery research. Herein, we report a one-step, light-promoted, three-component radical-coupling method for rapidly generating difunctionalized benzylalcohol-, aldehyde-substituted BCPs from aryl aldehydes, ethers, and [1.1.1]propellane. The method, which does not require metals or photocatalysts, features a broad substrate scope (58 examples) and excellent functional group tolerance. Furthermore, this protocol can be scaled up to the gram-level. Remarkably, these transformations are external-oxidant-free, thus exemplifying an environmentally friendly and practical synthetic strategy. [ABSTRACT FROM AUTHOR]

Chitosan is readily available from various biomass waste streams including crustaceans, cephalopods, insects, and fungus. The polymer possesses primary amine groups which are great handles for functionalization. Yet efficient functionalization with high degree of substitution is challenging to achieve via solvothermal methods due to limitations in chitosan solvation properties. Herein we report a mechanochemical and aging-based method directly addressing this point. Working in the solid phase helps stabilize the formation of Schiff bases from chitosan and aldehydes, affording a novel pathway to the green functionalization of chitosan by reductive alkylation, with unprecedentedly high degrees of substitution. The method showed great efficacy and compatibility for chitosan to be functionalized with 21 different aldehyde substrates and a low process mass intensity (PMI) of 36. This work also opens a new avenue for the development of mechanochemical and aging-based reductive amination transformations. [ABSTRACT FROM AUTHOR]

A water-mediated and Rh-catalysed one-pot multi-step synthesis of chiral 1,3-diarylpropan-1-ols is presented. This protocol utilizes readily available terminal alkynes and aldehydes as reaction partners, and features mild conditions, easy operation and water as the sole solvent, thus serving as an ideal means for the efficient synthesis of chiral 1,3-diarylpropan-1-ols. Control experiments suggested that the formation of chalcone intermediate followed by a double reductive process is crucial for the success of the reaction. This catalytic methodology could be easily scaled up for gram-scale synthesis with up to 10 000 S/C and the resulting products can be used to easily derive various bioactive molecules. [ABSTRACT FROM AUTHOR]

Triazine derivatives, a class of electron-deficient π-conjugated molecules with high photochemical activity and excellent luminescent characteristics, have been utilized as a kind of electron-acceptor for the construction of molecular cages, luminescent and photochromic materials. In this paper, a novel and highly stable MOF with cubane-like clusters, [Co4(SO4)3(F)3(tpt)2(tatb)] (1) (tpt = 2,4,6-tris-(4-pyridyl)-1,3,5-triazine, H3tatb = 4,4′,4′′-(1,3,5-triazine-2,4,6-triyl)tribenzoic acid), has been successfully synthesized based on a triazine derivative, and possesses unprecedented sulfate- and fluoride-bridged cubane-type tetranuclear cobalt clusters and a 3D + 3D → 3D open framework. Compound 1 shows a rather high BET surface area and exhibits excellent thermal stability and high chemical stability in common solvents and even in acidic or basic solutions (in a pH range from 4 to 12). Moreover, catalytic measurements show that compound 1 is an excellent heterogeneous catalyst for the selective oxidation of aryl alkenes to aldehydes or ketones with conversions of 97%. [ABSTRACT FROM AUTHOR]

This manuscript describes the synthesis of a triazolyl-pyridine-based phosphine, N-((diphenylphosphaneyl)methyl)-N-methyl-6-(1-phenyl-1H-1,2,3-triazol-4-yl)pyridin-2-amine, [2,6-{(PPh2)CH2N(Me)(C5H3N)(C2HN3C6H5)}] (1) (here onwards referred to as PNN) and its cationic and neutral MnI complexes and catalytic applications. The reaction of 1 with Mn(CO)5Br afforded a cationic complex [Mn(CO)3(PNN)]Br (2), which is highly stable in solid state, but in solution it gradually loses one of the CO groups to form a neutral complex [Mn(CO)2(PNN)Br] (3). Complex 2 on treatment with AgBF4 also yielded a cationic complex [Mn(CO)3(PNN)]BF4 (4). These complexes efficiently promoted the synthesis of quinoline derivatives via acceptor-less dehydrogenative coupling of 2-aminobenzyl alcohol and ketones, with complex 3 showing the highest activity with a very low catalyst loading (0.03 mol%) at 110 °C. Complex 3 (0.5 mol%) also showed excellent catalytic activity in the transfer hydrogenation of ketones and aldehydes to form respective secondary and primary alcohols. [ABSTRACT FROM AUTHOR]

A metal-free C–H functionalization of purines with aldehydes was developed to access C6-acylated purines via green radical reactions. Theoretically, there are many competitive reactions due to the three C–H bonds (C2–H, C6–H, C8–H) in the purine, and the acylation only happens at the purinyl C6-position. This method avoids a metal catalyst and provides a green approach to construct C–C (sp2) bonds at the purinyl C6-position, while maintaining excellent compatibility with various functional groups. Moreover, the protocol features broad substrate scope and easy scale-up. The transformation of the product demonstrates the significant practical value of the method. The primary mechanism was proposed based on controlled experiments. [ABSTRACT FROM AUTHOR]

A convenient method for Z → E geometry isomerization of aryl–aryl (stilbenes), alkyl–aryl, and alkyl–alkyl alkenes was developed. This user-friendly method utilized a popular commercial Hoveyda–Grubbs ruthenium olefin metathesis catalyst in the presence of sodium formate in toluene and is characterized by good functional group compatibility, including halogen, ester, aldehyde, and acetal functions. This research originated from trials on the valorization of a waste by-product resulting from the industrial synthesis of a valuable API—rosuvastatin. [ABSTRACT FROM AUTHOR]

Chiral β-amino alcohols are crucial building blocks in the synthesis of pharmaceutically active molecules and natural products. Developing green and sustainable methods for synthesizing chiral β-amino alcohols from renewable feedstocks continues to pose a significant challenge. Herein, we proposed a simple one-pot two-stage artificial cascade biocatalysis system for highly efficient conversion of renewable biomass-derived aldehydes into chiral β-amino alcohols with good yields and excellent enantioselectivity via sequential hydroxymethylation and asymmetric reduction amination. The initial stage involves converting aldehydes into α-hydroxy ketones by providing formaldehyde through benzaldehyde lyase-catalyzed hydroxymethylation. The subsequent stage is to convert α-hydroxy ketones into chiral β-amino alcohols through amine transaminase-catalyzed asymmetric reduction amination. Combining the two different types of reactions with two different enzymes, biomass-derived furfural 1a could be easily converted into (R)-2-amino-2-(furan-2-yl)ethanol ((R)-3a) and (S)-2-amino-2-(furan-2-yl)ethanol ((S)-3a) with up to 95% and 92% conversions and >99% ee, respectively. In addition, with this cascade biocatalysis, several enantiopure arylglycinols 3b–e were synthesized (39.4–99.0% conversions and >99% ee) from the biomass-derived benzaldehydes (1b–c) and benzaldehyde derivatives (1d–e). Furthermore, biotransformation on a preparative scale gave (S)-3a and (R)-3a in good yields (64.6% and 60.4%) and excellent ee (>99%). This study presents an eco-friendly and sustainable approach for synthesizing chiral β-amino alcohols using biomass-derived aldehydes. [ABSTRACT FROM AUTHOR]

The Friedel–Crafts arylation is among the most known organic reactions, usually being promoted by a Lewis acid, that have been employed for the synthesis of bis-indolyl methanes. Herein, we report a mild, inexpensive, green and organocatalytic protocol for the promotion of a Friedel–Crafts-type reaction between indoles and aldehydes, where N-heterocyclic iod(az)olium salts are utilized as halogen-bonding catalysts, leading to the double addition of the indole motif. A variety of aliphatic and aromatic aldehydes were converted into diarylmethanes in good to high yields, while the scope of indoles was also investigated. Water was employed as the solvent, while the reaction time was short. The reaction mechanism was also studied. [ABSTRACT FROM AUTHOR]

This study presents the utilization of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) radical-immobilized metal–organic frameworks (MOFs) for the oxidative cyclization of aldehydes and aminophenols, leading to the heterogeneous synthesis of 2-substituted benzoxazole molecules. The TEMPO-immobilized MOFs are successfully employed in one-pot sequential aerobic oxidation and oxidative cyclization reactions that enable the synthesis of 2-phenyl benzoxazoles from readily available benzyl alcohols and ortho-aminophenol precursors. The modified MOFs exhibit exceptional reactivity towards benzoxazole synthesis, demonstrating a wide range of substrate compatibilities and efficient performance under simple reaction conditions. Through the implementation of a mixed-ligand approach, precise control over the molar fraction and density of TEMPO radicals is achieved. Among the synthesized catalysts with radical density control, UiO-68-(TEMPO)1.0, which features the complete immobilization of TEMPO, displays the highest catalytic efficiency in the oxidative cyclization process. This enhanced performance can be attributed to the dual involvement of TEMPO species in the proposed reaction mechanism for oxidative cyclization. Notably, the MOF-TEMPO catalyst can be recycled up to five times without any loss of catalytic activity or crystallinity. This research is significant because the sequential approach proposed in this study bridges the TEMPO-catalyzed aerobic oxidation of alcohols and TEMPO-catalyzed oxidative cyclization of aldehydes with aminophenols under the same TEMPO catalyst and O2 atmosphere. [ABSTRACT FROM AUTHOR]

The Hofmann and Curtius rearrangements have been widely used in organic synthesis and developed for the industrial production (5–100 kg) of pharmaceutically relevant amines/amides. However, the existing use of a stoichiometric organic oxidant [(diacetoxyiodo)benzene or trichloroisocyanuric acid for the Hofmann rearrangement] for amides or an activating reagent (diphenylphosphoryl azide for the Curtius rearrangement) for carboxylic acids is environmentally unfriendly and economically less attractive. Herein, we report the first green oxidation of amides and aldehydes with oxone and halide (and NaN3) to generate N-halo amides and acyl azides, respectively, both of which rearrange into the common isocyanate intermediates and subsequently produce stable carbamates or ureas (the Hofmann and Curtius rearrangements) when trapped with alcohols or amines. This unified green approach is highly efficient as demonstrated by more than 30 examples for each rearrangement. Importantly, this approach generates inorganic nontoxic K2SO4 as the only byproduct, which is advantageous over the existing methods that produced stoichiometric, toxic, and organic iodobenzene, and chloro-isocyanuric acid, or diphenylphosphoric acid. Notably, three urea-based drugs and eight chiral urea catalysts were efficiently synthesized from corresponding aldehydes by this green oxidative Curtius rearrangement. This green oxidative approach for the Hofmann and Curtius rearrangements is expected to find wide applications in organic synthesis and process chemistry. [ABSTRACT FROM AUTHOR]

Autoxidation of aldehydes to peracids and carboxylic acids holds a significant impact in both academia and industry due to their wide applications in organic synthesis and environmental remediation. However, the multiple pathways involved in this reaction have hindered the development of sustainable methods for peracid synthesis. Herein, we conduct a comprehensive kinetic and mechanistic investigation to elucidate the interplay between these pathways. Subsequently, we introduce an efficient eco-friendly method to oxidize aldehydes to their corresponding peracids under sunlight or UV irradiation using oxygen as the sole oxidant without any additives or photocatalysts. Additionally, we demonstrate a simple method for the autoxidation of aldehydes to carboxylic acids via controlling key parameters such as the wavelength and solvent. These methods exhibit broad applicability to aromatic and aliphatic aldehydes, successful scaling up to the gram scale, and utilizing renewable solar energy making them good alternatives for traditional methods. [ABSTRACT FROM AUTHOR]

Solar energy-induced cascade/tandem reactions in one-pot are sustainable and green. Herein, the Pd/ NiTi-LDH nanocomposite, with Pd nanoparticles (NPs) (∼3–6 nm) deposited on NiTi-LDH nanosheets, was obtained and was applied in the reaction between nitro aromatics and alcohols to synthesize secondary amines under visible light. The superior performance observed over the as-obtained Pd/NiTi-LDH nanocomposite for this reaction can be attributed to a successful merging of Pd-based hydrogenation and LDH-based photocatalysis, in which consecutive light-induced hydrogenation of nitro compounds to amines, dehydrogenation of alcohols to aldehydes, condensation between the in situ formed aldehydes and amines to imines and the hydrogenation of final imines to generate the desired secondary amines were realized in one pot over Pd/NiTi-LDH under visible light. This work shows an effective and green strategy in the synthesis of secondary amines. This study also demonstrates the high potential of using metal/LDH nanocomposites for light-initiated organic syntheses. [ABSTRACT FROM AUTHOR]

A green and efficient method for the construction of functionalized 2,3-dihydrothiophene derivatives in water was reported. In this work, Novozym 435 acted as a remarkable biocatalyst in catalyzing the four-component reaction of aldehydes, malonitrile or ethyl cyanoacetate, 1,3-thiazolidinedione, and amines under mild conditions. Excellent yields (85–95%) of all the corresponding products could be obtained in reasonable reaction time. Moreover, Novozym 435 could be reused for six cycles with a yield of at least 80%. The rationality of this multicomponent reaction mechanism was also verified via control experiments. [ABSTRACT FROM AUTHOR]

In this study, three novel binuclear, distinctly defined, air-stable cobalt(II) complexes, denoted by the formulas [Co(H2L1)]2(1), [Co(H2L2)]2(2) and [Co(H2L3)]2(3), are reported. Binuclear cobalt(II) complexes (1–3) namely bis-[3,3′-bis[(2,6-dimethyl-phenylimino)-methyl]-[1,1′]-biphenyl-2,2′-dioxo cobalt(II)] (1), bis-[3,3′-bis[(2,6-di-i-sopropylphenyl)imino)methyl)-[1,1′-biphenyl]-2,2′-dioxodicobalt(II)] (2) and bis-[3,3′-bis[(2,6-diethyl-phenylimino)-ethyl]-[1,1′]-biphenyl-2,2′-dioxo cobalt(II)] (3) were synthesised and isolated for the first time. Several techniques, including mass spectrometry, UV-visible spectra, FT-IR spectra, elemental analysis, and single-crystal X-ray diffraction, were used to ascertain the structural properties of the binuclear cobalt(II) complexes. All these binuclear cobalt(II) [Co(H2L1)]2, [Co(H2L2)]2 and [Co(H2L3)]2 complexes (1–3) demonstrated excellent catalytic activity for the acceptor-less dehydrogenation (AD) reaction of primary alcohols to create the corresponding aldehydes and molecular hydrogen (H2). Multiple alcohols, including those that are electron-rich/electron-poor primary alcohols, have been successfully converted into the corresponding aldehydes using catalytic acceptor-less dehydrogenation (CAD), which only produces molecular hydrogen as a byproduct. [ABSTRACT FROM AUTHOR]

The influence of the P–M–P bite angle in diphosphine ligands on selectivity has been observed in various catalytic reactions. A better understanding of the ligand bite angle concept is important for the rational design of efficient catalytic systems. In the present work, the mechanism of cobalt-catalyzed C–H functionalization of aldehydes with enynes and how the diphosphine ligands alter regioselectivity were investigated by density functional theory (DFT) calculations. The catalytic cycle is initiated by the oxidative cyclization of enynes rather than the oxidative addition of aldehydes. Regioselectivity arises from competing σ-bond metathesis and migratory insertion steps, in which the steric effects of diphosphine ligands are the dominant factors influencing the activation barriers. The calculations indicate that σ-bond metathesis is more challenging and its feasibility is highly dependent on the ligand bite angle. The improved mechanistic understanding will enable further design of transition-metal-catalyzed selective cyclization reactions. [ABSTRACT FROM AUTHOR]

Acylethynylpyrroles, readily available from acylbromoacetylenes and pyrroles, smoothly undergo [3+2]-cyclization with ketones and aldehydes (room temperature) to give acylmethylidenepyrrolo[1,2-c]oxazoles. The reaction protocol meets the principles of the PASE (pot, atom, and step economy) paradigm to afford various pyrrolo[1,2-c]oxazoles, including spirocyclic ones, in up to 82% yield. [ABSTRACT FROM AUTHOR]

In this study, a novel magnetically recoverable Fe3O4@SiO2–BenzIm-Fc[Cl]/BiOCl nano-composite was synthesized using a simple chemical co-precipitation method. This is the first time that a magnetic nano-catalyst bearing ionic liquid, ferrocene and BiOCl is synthesized. The Fe3O4@SiO2–BenzIm-Fc[Cl]/BiOCl nano-composite was characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FE-SEM) techniques. The catalytic activities of the novel magnetic nano-composite were evaluated in one-pot three-component synthesis of a wide variety of 2-amino-3-cyano-4H-chromene derivatives under ultrasound irradiation. A simple, facile and highly efficient ultrasound-assisted method was developed to synthesize 4H-chromene derivatives via one-pot, three-component reaction of aldehyde, malononitrile and active phenolic compounds (2-naphthol, 1-naphthol, 3-(dimethylamino)phenol, resorcinol and orcinol) at room temperature. The reaction of aldehyde, malononitrile and orcinol is newly introduced in this paper. The ultrasound-assisted synthesis protocol that was studied in this article exhibits some notable advantages such as short reaction times, operational simplicity, green reaction conditions, high yields and easy work-up and purification steps. In addition, the novel magnetic nano-composite could be easily recovered by an external magnetic field and reused for six-reaction cycles without significant loss of its catalytic activity. [ABSTRACT FROM AUTHOR]

Aldehyde deformylation is an important reaction in biology, organic chemistry and inorganic chemistry and the process has been widely applied and utilized. For instance, in biology, the aldehyde deformylation reaction has wide differences in biological function, whereby cyanobacteria convert aldehydes into alkanes or alkenes, which are used as natural products for, e.g., defense mechanisms. By contrast, the cytochromes P450 catalyse the biosynthesis of hormones, such as estrogen, through an aldehyde deformylation reaction step. In organic chemistry, the aldehyde deformylation reaction is a common process for replacing functional groups on a molecule, and as such, many different synthetic methods and procedures have been reported that involve an aldehyde deformylation step. In bioinorganic chemistry, a variety of metal(iii)-peroxo complexes have been synthesized as biomimetic models and shown to react efficiently with aldehydes through deformylation reactions. This review paper provides an overview of the various aldehyde deformylation reactions in organic chemistry, biology and biomimetic model systems, and shows a broad range of different chemical reaction mechanisms for this process. Although a nucleophilic attack at the carbonyl centre is the consensus reaction mechanism, several examples of an alternative electrophilic reaction mechanism starting with hydrogen atom abstraction have been reported as well. There is still much to learn and to discover on aldehyde deformylation reactions, as deciphered in this review paper.

A new series of cationic ruthenium(II) complexes, [RuCl(PPh3)2(κ3-NNN-L1)]Cl (1), [RuH(PPh3)2(κ3-NNN-L2)]Cl (2), and [RuH(PPh3)2(κ3-NNN-L3)]Cl (3), bearing a 2,6-bis (1-R-5-methyl-pyrazol-3-yl) pyridine ligand (L1: R = H, L2: R = C6H4-p-CF3, L3: R = C6H4-p-OCH3), were synthesized and characterized with NMR, HRMS, and single-crystal X-ray diffraction. Their catalytic application was investigated in the acceptorless dehydrogenation (AD) of primary alcohols. Complex 1 outperformed 2 and 3 in terms of the selectivity towards the aldehydes, and provided the aldehydes with a yield of up to 99%, with good functional group tolerance under mild conditions. In addition, the only by-product of the reaction was dihydrogen, which can be collected as clean energy, and the reaction meets the requirements of environment-friendly chemistry. Complex 1 also proved to be a promising catalyst in the sequential AD/condensation reaction between the primary and secondary alcohols, affording α,β-unsaturated ketones in moderate to good selectivity. [ABSTRACT FROM AUTHOR]

Analysis of volatile organic compounds (VOC) within exhaled breath is subject to numerous sources of methodological and physiological variability. Whilst breathing pattern is expected to influence the concentrations of selected exhaled VOCs, it remains challenging to investigate respiratory rate and depth accurately in awake subjects. Online breath sampling was performed in 20 mechanically ventilated patients using proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). The effect of variation in respiratory rate (RR) and tidal volume (TV) on the VOC release profiles was examined. A panel of nineteen VOCs were selected, including isoprene, acetone, propofol, volatile aldehydes, acids and phenols. Variation in RR had the greatest influence on exhaled isoprene levels, with maximum and average concentrations being inversely correlated with RR. Variations in RR had a statistically significant impact on acetone, C3–C7 linear aldehydes and acetic acid. In comparison, phenols (including propofol), C8–C10 aldehydes and C3–C6 carboxylic acids were not influenced by RR. Isoprene was the only compound to be influenced by variation in TV. These findings, obtained under controlled conditions, provide useful guidelines for the optimisation of breath sampling protocols to be applied on awake patients. [ABSTRACT FROM AUTHOR]

A series of manganese(I) carbonyl complexes bearing structurally related NN- and NNN-chelating ligands have been synthesized and assessed as catalysts for transfer hydrogenation (TH). Notably, the NN-systems based on N-R functionalized 5,6,7,8-tetrahydroquinoline-8-amines, proved the most effective in the manganese-promoted conversion of acetophenone to 1-phenylethanol. In particular, the N-isopropyl derivative, Mn1, when conducted in combination with t-BuONa, was the standout performer mediating not only the reduction of acetophenone but also a range of carbonyl substrates including (hetero)aromatic-, aliphatic- and cycloalkyl-containing ketones and aldehydes with especially high values of TON (up to 17 200; TOF of 3550 h−1). These findings, obtained through a systematic variation of the N-R group of the NN ligand, are consistent with an outer-sphere mechanism for the hydrogen transfer. As a more general point, this Mn-based catalytic TH protocol offers an attractive and sustainable alternative for producing alcoholic products from carbonyl substrates. [ABSTRACT FROM AUTHOR]

The unique and highly tunable photophysical, photochemical and photoredox properties of porphyrins contribute to their versatile applications in alternate energy generation, sensing, and therapeutic fields. The synthetic route for meso substituted porphyrins involves acid-catalysed condensation of aldehyde and pyrrole followed by oxidation. Herein, we report an environmentally benign novel approach for the synthesis of substituted tetraaryl porphyrins using acetonitrile as the solvent and Keggin type phosphovanadotungstic acid as the catalyst. The simple one-pot strategy completely avoids the usage of acidic/chlorinated solvents and expensive oxidising agents. A reasonable spectroscopic yield of around 12–39% could be obtained for various derivatives under the optimised conditions. [ABSTRACT FROM AUTHOR]

Silica-based mesoporous materials, such as SBA-15, are important supports in the field of catalysis due to their ordered pore channels. The traditional synthesis route of SBA-15 suffers from high autogenous pressure and explosion risks, limiting its industrial production. Herein, a reflux system under ambient pressure was used for the synthesis of SBA-15. Ni nanoparticles were incorporated into the obtained materials to evaluate the quality of the SBA-15 support. The comparative performance of Ni/SBA-15H and Ni/SBA-15R validated there was negligible difference between the SBA-15 prepared by the hydrothermal method (SBA-15H) and the reflux method (SBA-15R). This revolutionary synthesis methodology provides a novel and secure route for the large-scale preparation of SBA-15. [ABSTRACT FROM AUTHOR]

4-Isoxazolines are important motifs in various biologically interesting molecules and versatile synthons for the preparation of various cyclic and acyclic compounds. Herein, two green and facile protocols were reported for the synthesis of a wide range of polyfluoroalkanesulfinyl or alkylsulfinyl 4-isoxazolines. A variety of aldehyde and ketone derived nitrones reacted with α-alkynyl sulfoxides under catalyst- and solvent-free conditions at room temperature to provide a series of polyfluoroalkanesulfinyl or alkylsulfinyl 4-isoxazolines with high efficiency. The synthesis of these sulfinyl 4-isoxazolines was further improved to a one-pot process in aqueous medium starting from aldehydes and hydroxylamine hydrochlorides without the need for isolating the nitrones. The reactions developed in this work are easy to perform and demonstrate significant ecological advantages. [ABSTRACT FROM AUTHOR]

n → π* has emerged as an important noncovalent interaction that can affect the conformations of both small- and macromolecules including peptides and proteins. Carbonyl-carbonyl (COCO) n → π* interactions involving CO groups are well studied. Recent studies have shown that the COCO n → π* interactions are the most abundant secondary interactions in proteins with a frequency of 33 interactions per 100 residues and, among the various secondary interactions, n → π* interactions are expected to provide the highest enthalpic contributions to the conformational stability of globular proteins. However, n → π* interactions are relatively weak and provide an average stabilization of about 0.25 kcal mol-1 per interaction in proteins. The strongest n → π* interaction could be as strong as a moderate hydrogen bond. Therefore, it is challenging to detect and quantify these weak interactions, especially in solution in the presence of perturbation from other intermolecular interactions. Accordingly, spectroscopic investigations that can provide direct evidence of n → π* interaction are limited, and the majority of papers published in this area have relied on X-ray crystallography and/or theoretical calculations to establish the presence of this interaction. The aim of this perspective is to discuss the studies where a spectroscopic signature in support of n → π* interaction was observed. As the "n → π* interaction" is a relatively new terminology, there remains the possibility of there being earlier studies where spectroscopic evidence for n → π* interactions was obtained but it was not discussed in light of the n → π* terminology. We noticed several such studies and, as can be expected, these studies were often overlooked in the discussion of n → π* interactions in the recent literature. In this perspective, we have also discussed these studies and provided computational support for the presence of n → π* interaction.

A series of alkynyl aryl conjugated aldehydes and imines were prepared and their adducts with various Lewis acidic boranes have been studied via NMR, absorption, and luminescence spectroscopies in solution. The imine-B(C6F5)3 adduct showed remarkable solution stability, and was then trialled in vapochromism experiments using simple impregnated paper strips to examine the fluorescence responses. [ABSTRACT FROM AUTHOR]

The use of the renewable platform molecule 5-hydroxymethylfurfural (HMF) in the multi-component Biginelli reaction has been investigated. Multicomponent reactions (MCR) using HMF offer straightforward access to novel fine chemicals. However, the peculiar reactivity and lower stability of HMF have limited its use in such strategies. In this paper, we report our results on the use of HMF in 3-component Biginelli reactions, leading in one single step to a series of functionalized dihydropyrimidinones obtained in moderate to good yields, with a broad substrate scope of 1,3-dicarbonyl compounds and urea building blocks. This is the first report on the use of HMF in this reaction. The CH2OH motif found in HMF provides useful functionalization for the target molecules, which cannot be offered by simpler aldehydes such as furfural. [ABSTRACT FROM AUTHOR]

The chemical stability of zeolitic imidazolate framework-8 (ZIF-8) in water, acid, base and organic solvent has been widely investigated. However, whether it is stable in aldehydes, which are common reactants, has rarely been considered. Herein, the partial or whole dissolution of ZIF-8 with 50 nm and 1000 nm sizes was observed in crotonaldehyde under air conditions. More importantly, the residual ZIF-8 gradually evolved from the original rhombic dodecahedra into a new octahedron morphology and still preserved the ZIF-8 phase structure. A series of experiments revealed that the essence of ZIF-8 degradation in crotonaldehyde is the presence of H+, derived from the autoxidation of crotonaldehyde exposing in the air to the corresponding acids. H+ could preferentially attack the Zn–N coordination bond located at the {211} edge and {111} vertices with {110} facet shrinkage of the rhombic dodecahedra, leading to the morphological reconstruction of ZIF-8. A further dynamic track showed that the dissolved ratio of ZIF-8 highly depended on the acidic value of crotonaldehyde, temperature and contact time. The dissolution process followed a shrinking core model and was controlled by the diffusion of the H+ step. [ABSTRACT FROM AUTHOR]

Transition metal coordination chemistry and catalysis are rife with phosphine ligands. One of the rather less studied members of the phosphine ligand family are phosphine aldehydes. We have synthesised 3-(diphenylphosphino)propanal (PCHO) with a slight modification of the known procedure and studied its complexation behaviour with palladium(II) and platinum(II). The catalytic activity of the palladium(II) phosphine aldehyde complexes was investigated in Cu-free Sonogashira and Suzuki–Miyaura cross-coupling reactions. Furthermore, the homogeneous nature of the catalytically active species was confirmed. [ABSTRACT FROM AUTHOR]

We report a Cu(I)-catalyzed synthesis of quinazolines via cascade cyclization/hydrodehalogenation by using acetamide as a nitrogen source and H2O as a hydrogen source. The current reaction provides a unified modular route from readily available starting materials to quinazolines in which aryl aldehydes can be decorated with diverse substitutions. In this reaction, acetamide becomes an interesting alternative for the unpleasant smelling ammonia and toxic amidines. [ABSTRACT FROM AUTHOR]

Ligand-free reductive coupling of aldehydes with 1,3-dienes was successfully developed using the nickel nanoparticle catalyst SANi (sulfur-modified Au-supported nickel). Leakage of nickel species into the reaction solution is minimal. SANi can be used repeatedly and the reaction is an environmentally benign reaction. [ABSTRACT FROM AUTHOR]

Facile reductions of carboxylic acids to aldehydes or alcohols can be effected under mild conditions upon initial conversion to their corresponding S-2-pyridyl thioesters. Upon treatment with a commercially available and air-stable nickel pre-catalyst and silane as a stoichiometric reductant, aldehydes are formed in moderate to good yields. Alternatively, the 1-pot conversion of acids to their thioester derivatives can be followed by reduction to the alcohol upon treatment with sodium borohydride. A variety of starting materials ranging from highly functionalized acids to educts from the Merck informer library can be transformed using these green reaction media. [ABSTRACT FROM AUTHOR]

This paper describes an atom-economical strategy for the direct conversion of Baylis–Hillman alcohols to β-chloro aldehydes under metal free conditions with excellent functional group tolerance. The use of stable-nontoxic Oxone as a terminal oxidant along with an inexpensive salt (sodium chloride) as a halogen source and water as the reaction medium makes this chemical synthetic process more viable and environmentally benign contributing towards green chemistry. [ABSTRACT FROM AUTHOR]

A concise and practical approach for expedient synthesis of substituted benzoxazolpyrroles, benzothiazolpyrroles and indolizines by three-component cascade annulative coupling of an aldehyde, 2-heteroaryl acetonitrile and an isocyanide in the presence of 10 mol% 2-(hydroxymethyl)pyrrolidinium acetate has been devised in high yields for the first time. The compatibility with a wide range of functional groups makes this domino formation of one C-C and two C-N bonds interesting. In particular, the heterocycles derived from 2-bromobenzaldehydes are further converted into indole-fused novel pentacyclic (6-5-5-5-6) heteroaromatic compounds by Pd(II)-catalyzed intramolecular N-arylation via a cross-dehydrobromination reaction. This annulative protocol not only provides an efficient method to access tricyclic heteroaromatics, but also enriches the research domain of pentacyclic scaffolds. [ABSTRACT FROM AUTHOR]

Although transition metal catalyzed dehydrogenative cross-coupling reactions have achieved great success for accessing carbon–carbon and carbon–heteroatom bonds during the past decade, metal-free acceptorless dehydrogenative cross coupling is still scarce and highly desirable. Herein we report a robust metal-free acceptorless dehydrogenative cross-coupling for both carbon–heteroatom and carbon–carbon bond formation. By synergistic catalysis of the organophotocatalyst 4CzIPN and a thiol under blue light irradiation, the cross-coupling of aldehydes with alcohols or of two different alcohols proceeds smoothly with a broad substrate scope and good functional group compatibility, providing the corresponding esters in satisfactory yields along with the release of hydrogen gas. A dehydrogenative intramolecular acylation leading to fluorenone derivatives is also realized by this metal-free redox-neutral process. Mechanistic studies indicate the generation and subsequent oxidation of an acyl radical to its cation under photocatalytic conditions. [ABSTRACT FROM AUTHOR]