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The New Journal of Chemistry, published by the Royal Society of Chemistry and the Centre National de la Recherche Scientifique, features a collection of papers covering various topics in chemistry. The papers focus on specific research studies and provide detailed information on methods and results. Topics include catalysis, nanomaterials, photocatalysis, and electrochemistry. Written by authors from different institutions, these papers offer a comprehensive overview of recent research in the field of chemistry. [Extracted from the article]

Quinones are valuable structural motifs found in numerous natural products and pharmaceuticals. In particular, p-benzoquinones are of great interest because of their ready availability and versatile reactivity. They can serve as good Michael acceptors and participate in many cycloaddition, nucleophilic addition and multicomponent reactions. However, the construction of polycyclic architectures with increased stereochemical features is another perspective of quinone chemistry. The present review summarizes the recent advances (2018–2023) in stereoselective annulation involving p-benzoquinones for the construction of fused, spiro and bridged/cage frameworks. In this regard, different types of annulations, such as [3+2], [3+3], [3+2+1], [4+2] and [2+2], are discussed for accessing diverse fused heterocycles in a stereoselective manner. Some novel annulation methods are reviewed for building spiro heterocycles and cage molecules. Most of the reactions described in this review are simple, providing quick formation of the desired products with high stereoselectivity. In this regard, typical reaction mechanisms are presented to understand how quinoidal scaffolds show variable reactivity towards reaction partners. [ABSTRACT FROM AUTHOR]

The current review describes different annulation strategies reported with electrophilic benzannulated heterocycles for accessing heteroacenes. For the past two decades, the chemistry of electrophilic benzannulated heterocycles was extensively investigated, and several dipolar cycloadditions, metal and organo-catalyzed transformations were introduced for the generation of fused heterocycles. In this review, we have collected all the reports where the annulation of electrophilic benzannulated heterocycles results in a fully aromatic system, viz. heteroacenes with tri-, tetra-, and pentacyclic rings. We reviewed every paper on the synthesis of fused heterocycles that was accessible and categorized the review into several parts based on the electrophilic benzannulated heterocycle used in the heteroacene synthesis such as electrophilic indole, electrophilic benzothiophene, and so forth. The generality and mechanistic postulates of each methodology are highlighted. In addition, we have also tried to feature the advantages or shortcomings of each method and have mentioned the possible applications of these methodologies for accessing heteroacenes for material applications. [ABSTRACT FROM AUTHOR]

A novel synthesis method has been developed for the construction of functionalized 2,4-diarylpyridines. The reaction involves several key processes, including a reduction reaction, Michael reaction, decarboxylation, intramolecular cyclization, oxidation, ring-opening and aromatization reaction. All of these processes are facilitated by heating a mixture of the starting materials in an environmentally benign solvent, propylene carbonate (PC), with the oxidant (air) and the catalyst Cu(OAc)2. This cascade reaction not only forms two new bonds but also cleaves three existing bonds in a single pot. The protocol presented in this study is a valuable tool for synthesizing functionalized unsymmetrical 2,4-diarylpyridines. [ABSTRACT FROM AUTHOR]

Indole structural motifs are ubiquitous in natural products, pharmaceuticals, agrochemicals and functional materials. The immense importance of the indole moiety, especially in the field of drug discovery, has fuelled continued attention in indole chemistry for over a century. In the recent past, a large number of metal-free methodologies have been developed apart from metal-catalyzed annulation processes. The present review focuses on recent (2019–mid-2023) efforts towards the construction of the indole core via transition-metal-free methods, which include acid-catalyzed, base-catalyzed, photochemical, electrochemical, iodonium-salt promoted, SOCl2/DMSO-mediated, uncatalyzed/thermally assisted and miscellaneous methods. The reactions described in this review mostly employed readily accessible starting materials, and inexpensive catalysts that are environmentally benign and easy to handle. In most cases, mechanistic aspects have also been highlighted for better understanding of the reaction pathways. Interestingly, some of the synthesized compounds mentioned in this review are potentially bioactive. [ABSTRACT FROM AUTHOR]

A sequential rhodium(III)-catalyzed spiroannulation and lactonization strategy has been developed for the synthesis of a highly rigid spirobenzosultam lactones in good yields with high regioselectivity by means of aromatic ortho-C–H bond activation/functionalization of 3-aryl N-sulfonyl ketimines with 4-hydroxy-2-alkynoates. The reaction proceeds through a cascade of C–H activation followed by spiroannulation and lactonization. In this approach, two C–C and C–O bonds are formed in a single step. This is the first report on the spiroannulation of cyclic N-sulfonyl ketimines with hydroxyalkynoates. [ABSTRACT FROM AUTHOR]

Non-alternant non-benzenoid hydrocarbons exhibit unique properties compared to their well-studied benzenoid counterparts. However, the synthesis of these structures with extended π-conjugation or their integration into established benzenoid frameworks presents ongoing challenges in organic chemistry. In this study, we investigated different strategies for the synthesis of π-extended, azulene-containing polyaromatic hydrocarbons (PAHs), the key challenge being the formation of intramolecular C–C bonds involving different positions of the azulene. The Pt-catalyzed alkyne benzannulation gave the best results as ring closure reactions have been accomplished simultaneously at the 1 and 5 positions of the azulene unit, allowing the preparation of three azulene-annulated anthracene structural isomers whose optical and electrochemical properties have been studied. Although the three isomers possess very similar properties in the neutral state, the mono- and diprotonated forms differ significantly with absorption extending up to the near-infrared region. [ABSTRACT FROM AUTHOR]

Herein, we report a Pd-catalyzed multicomponent cascade reaction of 3-diazo oxindole and isocyanides to synthesize N-fused polycyclic indoles consisting of an in situ generated amide-assisted regioselective [3+1+1] annulation reaction. Additionally, a mechanism is proposed and investigated using DFT that strongly favors the role of amide in assisting the annulation reaction, which is further confirmed using control experiments. [ABSTRACT FROM AUTHOR]

The synthesis of 3-methoxy-benzanthrones was achieved in two steps by Suzuki–Miyaura coupling and BBr3-promoted Friedel–Crafts acylation under mild conditions with an overall yield of 17–74% and tolerance toward various substrates using commercially available reagents. The competitive mechanism between demethylation and Friedel–Crafts acylation was first rationalized via a deuterium-labelling experiment and DFT calculations. Basic photochemical characteristics of 3-methoxy-benzanthrones and 3-hydroxy benzanthrones were investigated, and the benzanthrones were found to possess excellent photochemical properties. Additionally, using this novel strategy, alkaloid oxoglaucine with a similar tetracyclic skeleton was successfully synthesized with a 70% overall yield via two steps. [ABSTRACT FROM AUTHOR]

We present a density functional theory study to characterize the possible mechanisms and origins of regio- and stereoselectivities of N-heterocyclic carbene (NHC)-catalyzed reactions of 2-bromoenals with thioamides leading to the formation of 1,3-thiazin-4-ones. According to DFT results, the energetically favorable mechanism involves the following elementary steps: formation of a Breslow intermediate via coordination of the NHC to 2-bromoenal followed by 1,2-proton transfer. Debromination followed by 1,3-proton transfer generates the α,β-unsaturated acylazolium intermediate, which further undergoes thia-Michael addition to thioamide forming the enolate intermediate. Subsequent 1,5-proton transfer and intramolecular cyclization give the six-membered ring intermediate, which upon elimination of NHC leads to the formation of 1,3-thiazin-4-one. The thia-Michael addition step was identified as the regio- and stereoselectivity-determining step, affording the S-configurational product preferentially, in agreement with previous experimental observations. According to NCI analysis, the stronger non-covalent interactions such as CH⋯π, LP⋯π and π⋯π interactions lead to the lower energy of the transition state that corresponds to the major stereoisomer of 1,3-thiazin-4-one. [ABSTRACT FROM AUTHOR]

We present a novel green synthetic protocol for the construction of a broad range of substituted fused azabicyclo[3.3.1]nonadiquinoline scaffolds through a formic acid catalyzed formal [4 + 2] annulation/Mannich/dearomatization domino reaction. This unified strategy shows a broad substrate scope with high functional group tolerance, resulting in good to high yields under environmentally benign, transition-metal-free, low-cost, and operationally simple conditions. The current method outperforms existing methods in terms of green and sustainable conditions. The reaction mechanism was confirmed based on DFT calculations. [ABSTRACT FROM AUTHOR]

Chemical Communications is a journal published by The Royal Society of Chemistry that focuses on the chemical sciences. The current issue covers topics such as astrochemistry and advances in circularly polarized luminescence materials. The journal is published 100 times a year and is available in both print and electronic formats. The document also provides information for authors who want to submit their work for publication, including submission instructions and guidelines for reproducing published contributions. Additionally, it includes copyright information and permissions required for reproducing the publication. A list of previously published feature articles and communications is also provided. [Extracted from the article]

A facile [3+3] annulation method for the construction of fused α-carboline or indolo[2,3-c]isoquinoline frameworks from easily synthesizable N,N′-cyclic azomethine ylides and 3-diazoindolin-2-imines using a Ru(II) catalyst is reported. This strategy was found to be efficient and effective for the syntheses of a variety of fused polycyclic molecules with a wide substrate scope, mild reaction conditions, and good to excellent yields. In addition, the mechanistic pathway of this transformation has been investigated by performing various control experiments with ESI-MS analyses. [ABSTRACT FROM AUTHOR]

In the synthesis of medicinally and industrially valuable quinoline scaffolds, we report a one-pot greener synthetic route to do away with harsh reaction conditions, low productivity, and unstable substrates associated with the classical methods reported in the literature. Readily available alcohols undergo acceptorless dehydrogenative annulation in basic media over an engineered nitrogen-rich hollow-spherical microporous polymer (MOP-TA) devoid of any metal support. This affordable and sustainable route stands up to the test of scalability and green matrices, which are supported by various spectroscopic and microscopic techniques. [ABSTRACT FROM AUTHOR]

Chemical Communications is a journal published by The Royal Society of Chemistry that focuses on the chemical sciences. It covers a wide range of topics, including recent advancements in fluorescence-based chemosensing and chiroptical regulation of macrocyclic arenes. The journal is published 100 times a year and is available in both print and electronic formats. It provides information for authors who want to submit their work for publication, including instructions, guidelines for reproducing published contributions, and copyright information. The document also lists the titles and authors of articles that have been published in the journal. [Extracted from the article]

Supramolecular assemblies of pentacenequinone derivative 4 act as reactors, reducing agents and shape directing agents for the preparation of PANI@Au:CuO nanocomposites (NCS). The as-prepared PANI@Au:CuO NCS serve as recyclable photocatalysts to construct 2-arylbenzimidazole derivatives under mild conditions through sequential amination, azidation and annulation reactions (visible light irradiation, room temperature and aerial conditions). The present protocol emphasizes the role of assemblies of the pentacenequinone derivative as visible light harvesting materials as well as oxidants in multiple C–N bond formation reactions. To our delight, the reaction also worked well under natural sunlight. The mechanistic studies supported the in situ generation of H2O2 during the reaction. Further, a portable paper based “dip catalyst” has been developed for carrying out sequential amination, azidation and annulation reactions. [ABSTRACT FROM AUTHOR]

The detailed mechanism and the role of catalyst in the PPh3-catalyzed [3+6] annulation reaction of MBH carbonate and dicyanoheptafulvene have been systematically investigated using a DFT method. Based on the calculations, the transformation of MBH carbonate includes several steps: (1) nucleophilic addition of PPh3 to MBH carbonate, (2) cleavage of the C–O bond, (3) α-H elimination for the formation of allylic phosphorus ylide, (4) regioselective α-addition of allylic phosphorus ylide with dicyanoheptafulvene, (5) intramolecular ring-closure, and (6) regeneration of the PPh3 catalyst. The C–O bond cleavage is considered to be the rate-determining step and the reaction between allylic phosphorus ylide and dicyanoheptafulvene is the regioselectivity-determining step with the α-addition mode occurring prior to γ-addition. The value of local nucleophilicity calculated using the Parr function proves that the α-carbon is more reactive than γ-carbon thus leading to a lower energy barrier. NCI and AIM analyses also show that the transition states involved in α-addition possess stronger weak interactions, which are responsible for stabilizing the corresponding transition state. The ELF shows that PPh3 promotes the release of BocO− anions mainly by alleviating the electron density between the Cγ–O1 bonds. [ABSTRACT FROM AUTHOR]

Reported here is the CO2-facilitated radical sequential (3 + 2) annulation of 1,6-enynes that proceeds under the concerted catalysis of sulfinate and a photocatalyst (PC) to construct benzo-fused tricyclic scaffolds, that is tetrahydrofluorenes and their N-heterocyclic analogues, in generally good yields. This CO2-facilitated method allows the stable aromatic groups of 1,6-enynes to undergo radical addition-induced dearomatization and rearomatization under metal-, external oxidant- and base-free conditions and features a broad scope of 1,6-enyne substrates, as demonstrated by more than 60 examples including a series of 1,6-enyne derivatives of complex bioactive compounds. Importantly, CO2 as a green additive is disclosed to be essential for achieving this reaction with good efficiency, demonstrating a new role of CO2 in this transformation. [ABSTRACT FROM AUTHOR]

A highly efficient protocol for stereoselective synthesis of novel polycyclic benzo[b]thiophene derivatives was developed. Using quinine-derived bifunctional thiourea (5 mol%) as a catalyst, asymmetric [3+3] annulation of N-(benzo[b]thiophen-2-yl)-sulfonamide with 2-alkynyl cycloenone could provide dihydrobenzo[4,5]thieno[2,3-b]pyridine derivatives in moderate to good yields (up to 93%) with mostly excellent enantioselectivities (up to 97% ee) under mild conditions. In addition, large-scale experiments and derivatizations were explored. In particular, the target product in large-scale experiments could be easily purified by filtration and the filtrated product showed >99% ee. [ABSTRACT FROM AUTHOR]

Herein, we have realized an efficient and solvent-tunable Rh(III)-catalyzed [5+2] annulation of N-benzo[d]imidazole indolines with 2,2-difluorovinyl tosylate that presented an unusual 1,2-regioselectivity for the chemodivergent construction of monofluorinated and gem-difluorinated benzodiazepines, which are defined as potent anti-tumor agents against different cancer cell lines. In general, this work provides a powerful complement to both C–H activation chemistry and anti-tumor lead discovery. [ABSTRACT FROM AUTHOR]

The assembly of isocoumarins starting from easily available N,N-dimethyl enaminones and iodonium ylides via a Rh(III)-catalyzed C–H bond activation/annulation cascade reaction is herein described. This protocol proceeds under mild conditions and provides access to a wide variety of isocoumarin derivatives in good to excellent yields with good functional group compatibility. Furthermore, the gram-scale synthesis and various further chemical transformations enhance its synthetic utility. [ABSTRACT FROM AUTHOR]

The dehydrogenative [4 + 2] annulation is a step- and atom-economical way to construct benzo-fused six-membered rings which are prevalent in natural products, pharmaceuticals and agrochemicals. Herein, we disclosed a visible-light induced dehydrogenative [4 + 2] annulation of benzothioamides and alkynes, which was performed under mild aerobic conditions and catalyzed by the metal-free heterogeneous photocatalyst graphitic carbon nitride (g-C3N4). The heterogeneous photocatalysis proceeded smoothly with simple operation and under mild conditions and gave a variety of isothiochromenes in good yields. g-C3N4 displays excellent stability and recyclability for the photochemical reaction. The detailed mechanistic studies revealed that g-C3N4 promoted the formation of a sulfur centered radical under visible-light irradiation via a single electron transfer process. The radical intermediate further mediated a [4 + 2] annulation with alkynes to produce isothiochromenes. [ABSTRACT FROM AUTHOR]

The possible mechanism and origin of stereoselectivity of the NHC-catalyzed [3+4] annulation reaction between an enal and 5-alkenyl thiazolone leading to ε-lactone have been investigated using density functional theory (DFT) calculations. The reaction is identified to proceed via six elementary steps: the nucleophilic addition of the NHC to the enal (step 1), followed by the 1,2-proton transfer to form the Breslow intermediate (step 2). Addition to the other substrate 5-alkenyl thiazolone in which a new C–C bond is formed (step 3). Another proton transfer (step 4) followed by intramolecular cyclization leads to the [3+4] cycloadduct (step 5). The NHC regeneration completes the catalytic cycle and affords the desired product ε-lactone (step 6). DFT results show that the C–C bond formation step (step 3) is the stereoselective step and the RS-configurational isomer is the predominant product. The distortion–interaction analysis indicates that interactions between the two fragments control the stereoselectivity of the reaction. Further non-covalent interaction analysis shows that the cumulative interactions such as CH⋯N, CH⋯π, OH⋯O and CH⋯S are responsible for the stereochemistry of the reaction. The mechanistic insights gained in the present work should be useful for the rational design of a new catalytic reaction in the future. [ABSTRACT FROM AUTHOR]

In this paper, we developed a rhodium-catalyzed annulation of vinylene carbonate with amidines, leading to 4-methylquinazolines with moderate to excellent yields. This procedure proceeded by sequential ortho-acylation and annulation, where vinylene carbonate served as the acetylation reagent rather than the ethyne surrogate. [ABSTRACT FROM AUTHOR]

As a base structural unit, 1,4-dihydropyridines (DHPs) containing benzosultams widely exist in bioactive molecules and drugs. These compounds are generally synthesized by organic-base catalyzed methods that require specifically functionalized substrates or harsh conditions. Herein, a [3+3] annulation reaction of cyclic N-sulfonyl ketimine with various substituted isatylidene malononitrile or benzylidene malononitriles was documented. This biocatalytic strategy provides a green route for synthesis of 1,4-DHPs containing benzosultams, with good functional groups compatibility and yields. Under optimal conditions, lipase leads to the formation of 1,4-DHPs containing benzosultams in up to 87% yield. [ABSTRACT FROM AUTHOR]

The development of an electrochemical process method for the synthesis of P-chiral phosphine derivatives poses a considerable challenge. Here, we present an electricity-driven cobalt-catalyzed enantioselective C–H annulation of arylphosphinic amides and alkynes, which provides rapid access to P-chiral cyclicphosphorus oxides in good yields with excellent enantioselectivities (48–99% yields, 94–>99% ee). The reaction was compatible with aqueous solvents and proceeded efficiently in a shorter reaction time compared with the previous work using oxidants. The process employs a combination of readily available chiral salicyloxazoline and cobalt acetate tetrahydrate as an inexpensive catalyst. Notably, the kinetic resolution process was also achieved with s factors up to 347.8. Experimental, kinetic and computational studies on cobalta-electrocatalysis provide insights into the catalyst's working mode. [ABSTRACT FROM AUTHOR]

p-TsOH promoted annulation reaction of 3-(indol-3-yl)maleimides and (indol-2-yl)diphenylmethanols in chloroform afforded functionalized pyrrolo[3′,4′:6,7]cyclohepta[1,2-b:4,5-b′]diindoles in satisfactory yields, in which a formal [4+3] cycloaddition and an unprecedented rearrangement of the maleimide motif from the C3- to C2-position of the indole ring was firstly observed. Alternatively, the similar reaction of 3-(indol-3-yl)maleimides and 3-hydroxy-3-(indol-3-yl)-indolin-2-ones in acetonitrile gave functionalized spiro[indoline-3,9′-pyrrolo[3′,4′:4,5]cyclopenta[1,2-b]indole] in good yields and with high diastereoselectivity. On the other hand, p-TsOH promoted reaction of 3-(indol-3-yl)maleimides and 2-hydroxy-2-(indol-3-yl)-indene-1,3-diones gave functionalized spiro[indene-2,9′-pyrrolo[3′,4′:4,5]cyclopenta[1,2-b]indoles] as major products and spiro[indene-2,9′-pyrrolo[3′,4′:6,7]cyclohepta[1,2-b:4,5-b′]diindoles] as minor products. [ABSTRACT FROM AUTHOR]

A novel and unprecedented method for the polychlorinated alkylation annulation of N-arylacrylamide has been developed under electrochemical conditions with diazo salt as the mediator at the cathode reduction and CH2Cl2 as the substrate and solvent. Remarkably, it is benzene free radicals generated from the diazo salt under reductive electrolytic conditions that induce the hydrogen transfer of CH2Cl2, resulting in the formation of polychloromethyl radicals, which were transferred into the bulk phase solution and then reacted with the N-arylacrylamide substrate. This electrochemical diazo-salt-mediated protocol provides a broad range of functional tolerance and affords good yields for polychloromethyl indolone derivatives under ambient conditions at room temperature in a simple undivided cell. [ABSTRACT FROM AUTHOR]

1,2-Oxaphosphinane and 1,2-oxaphosphinine 2-oxides and their benzo derivatives, δ-phosphonolactones and δ-phosphinolactones, also called δ-phostones and δ-phostines, are important six-membered oxaphosphaheterocycles and crucial core structures of some biologically active compounds and organic materials. Numerous synthetic methods of these oxaphosphaheterocycles have been developed. They mainly focus on the cyclization strategies, including construction of P–O, O–C, P–C, and C–C bonds via cyclizations, and [4+2], [5+1], and [3+3] annulations. Cycloadditions, ring contractions and expansions have also been applied in the synthesis of 1,2-oxaphosphinane and 1,2-oxaphosphinine 2-oxide derivatives. In this review, we have described various strategies for the synthesis of 1,2-oxaphosphinane and 1,2-oxaphosphinine 2-oxide derivatives and further development. [ABSTRACT FROM AUTHOR]

A novel and transition metal-free synthesis of benzo-δ-phosphonolactams from readily available ethyl arylmethylphosphonochloridates and dibenzo[b,f][1,4]oxazepines was developed. The reaction includes tandem phosphonylation, deprotonation, intramolecular nucleophilic addition, and aromatization, affording various polycyclic benzo-δ-phosphonolactams in moderate to good yields and diasteroselectivity in one-pot (up to 96% yield and 83 : 17 dr). [ABSTRACT FROM AUTHOR]

A new mesoporous MCM-41-immobilized dichloro(pyridine-2-carboxylato)gold(III) complex [MCM-41-PicAuCl2] was synthesized via an addition reaction of a dichloro(3-hydroxypyridine-2-carboxylato)gold(III) complex to triethoxy(3-isocyanatopropyl)silane, followed by immobilization on MCM-41 and was characterized by different physico-chemical techniques. In the presence of 5 mol% of MCM-41-PicAuCl2, the annulation reaction between anthranils and ynamides proceeded smoothly under mild conditions to afford diverse 6- or 5-formylindoles with high atom economy and good to excellent yields. This new heterogenized gold(III) complex can be easily recovered through a simple filtration process and recycled more than seven times without any apparent loss of its catalytic efficiency. [ABSTRACT FROM AUTHOR]

Despite the widespread applications of amino phenazines, there is still lacking an efficient method enabling direct and diverse access to such compounds due to the limited availability of feedstocks and the challenge in controlling the synthetic selectivity. Here, by using a strategy of single electron oxidation (SEO) induced tandem dual C–H amination, we report a mild approach addressing the as-described issue via oxidative annulation of readily available anilines and o-phenylenediamines, which proceeds with a broad substrate scope and good functional group tolerance, directly uses primary amines as C–H aminating agents, employs a reusable nitrogen-doped carbon-supported cobalt nanocatalyst (Co-Nx/NC-800) and naturally abundant molecular O2, and exhibits excellent step and atom efficiency. The developed chemistry offers a practical platform to construct various promising amino phenazines that are difficult to synthesize with the conventional methods, and paves the way to further develop SEO-induced valuable transformations under sustainable heterogeneous base metal catalysis. [ABSTRACT FROM AUTHOR]

We present a computational study on the mechanisms and stereoselectivities of the [4+2] annulation of an enal with a pyrazolinone catalyzed by N-heterocyclic carbene (NHC). The computational results show that the catalytic reaction proceeds via eight steps: nucleophilic addition of the NHC to the enal (step 1) followed by 1,2-proton transfer affords the Breslow intermediate (step 2). C–Cl bond cleavage generates the enolene intermediate (step 3). Successive 1,5-proton transfer (step 4) and γ-C–H deprotonation (step 5) afford the vinyl enolate intermediate, which undergoes nucleophilic addition to the pyrazolinone, forming a new carbon–carbon bond (step 6). Intramolecular cycloaddition (step 7) followed by dissociation of the catalyst from the product (step 8) completes the whole catalytic cycle. For step 2, in addition to the direct proton transfer pathway, water- and HOAc-mediated proton transfer mechanisms have been explored, and HOAc was found to play an important role as the proton shuttle in forming the Breslow intermediate. Step 6 determines the stereoselectivity of the reaction. A cumulative effect of a number of noncovalent interactions (π⋯π, CH⋯O, CH⋯π and repulsion interactions) between the vinyl enolate intermediate and the pyrazolinone creates a difference in the enantioselectivity. The computed enantioselectivity (99% ee) agrees well with the value reported by experiments (99% ee). [ABSTRACT FROM AUTHOR]

We present a comprehensive DFT study of the mechanism for N-heterocyclic carbene (NHC)-catalyzed cycloaddition that uses indole-2-formaldehydes and isatins as substrates. After precatalyst activation, the catalytic reaction proceeds through six steps: initial coupling of NHCs with indole-2-formaldehydes, followed by 1,2-proton transfer. Then the resulting Breslow intermediate undergoes successive oxidization (by quinone DQ), N–H deprotonation, and [3+2] cycloaddition. The five-membered cycloadduct further undergoes NHC elimination to form the final product. For Breslow intermediate formation, besides the direct mechanism, the use of mediators (NEt3 and NEt3·H+) to promote proton transfer has been examined, and the energetically most preferred pathway is that promoted by the Brønsted acid NEt3·H+. The [3+2] cycloaddition determines the stereochemistry arising mainly from a combination of weak interactions (CH⋯O and lone pair (LP)⋯π) and produces (S)-N,O-aminal indole predominantly. Our DFT results align with previous experimental observations. The present study may provide some useful hints for the rational design of more stereoselective reactions and even the selection of catalysts and substrates. [ABSTRACT FROM AUTHOR]

A transition metal-catalyzed carbene insertion strategy has been developed to activate the inactivated sp2 C–H bond of medicinally important cis-stilbene acids. This approach enables the facile construction of α-pyrone and chromene-2-one skeletons on the olefinic bond of cis-stilbene acid with high atom economy, good yield, broad functional group tolerance and gram-scale synthetic feasibility. The strategy unveils the efficiency of acid functionalities as directing groups along with sulfoxonium and hypervalent iodonium ylide as carbene precursors. The constructed architectures were explored for their photophysical properties showing emission ranging from 500 to 600 nm, and the biological potential was examined through molecular docking analysis and percentage inhibition studies. Additionally, ESI-MS studies were also performed to identify the key intermediates, helping to sketch a probable mechanism. [ABSTRACT FROM AUTHOR]

An efficient synthetic route to indazole-fused dihydrophenanthridinones in excellent to almost quantitative yields under mild reaction conditions was developed. The reaction utilizes the acid-controlled Rh(III)-catalyzed C–H activation of 3-arylindazoles followed by their annulation with readily available hypervalent iodonium ylides. This methodology afforded a wide range of products that could be isolated using only a simple filtration without the need for column chromatography. In addition, the catalytic system can be recycled at least eight times with excellent yields, which may make it amenable to industrial production. Moreover, the photophysical properties of the synthesized dihydroindazolo[2,3-f]phenanthridin-5(6H)-ones indicate that they may have potential applications as new fluorescent materials. [ABSTRACT FROM AUTHOR]

The present work demonstrates an efficient ligand-free synthesis of diverse benzisothiazolones and benzisoselenazolones exploiting a magnetically retrievable nano-nickel ferrite catalyst in X–N (X = S, Se) cross-coupling with concurrent annulation of 2-iodobenzanilides and elemental sulphur or selenium. The protocol features the use of the recyclable nano-nickel ferrite catalyst, substrate diversity, cheap sulphur and selenium powder as chalcogenation agents, comparatively low reaction temperature and useful application of synthesized molecules. The rarely explored chemistry of NiFe2O4 towards the X–N cross-coupling reaction well complements conventional methods for the synthesis of S–N or Se–N heterocycles. Nickel ferrite nanoparticles were prepared by a simple hydrothermal method and characterized by using XRD, SEM, TEM, HRTEM, SAED, energy dispersive X-ray spectroscopy, XPS, ICP-AES and FT-IR analyses. The easy recovery of the catalyst and high product conversion make the protocol practically economic. The oxidation prone sulphur in benzisothiazolones is transformed into a variety of saccharin motifs using TBN and oxygen as the right oxidant combination. In addition, both the S–N and Se–N containing heterocycles are scaled up and further transformed into novel C–H functionalized products and selenol derivatives, respectively. [ABSTRACT FROM AUTHOR]

A facile, metal- and additive-free C–C bond construction between imidazo[1,2-a]pyridines and coumarin-3-carboxylic acids through a decarboxylative Michael addition is reported to achieve an imidazo[1,2-a]pyridin-3-yl-chroman-2-one skeleton. In addition, heterocyclic polyaromatic dibenzoisochromenoimidazo[1,2-a]pyridin-6-ones of value for future medicinal chemistry can be obtained successfully by this procedure through a domino reaction involving Michael addition/decarboxylation/oxidation/C–H bond activation and annulation. [ABSTRACT FROM AUTHOR]

Cyclic anhydrides, including sulfur-embedded anhydrides such as thiodiglycolic anhydride, are useful dipolar synthons for the synthesis of complex organic molecules through formal cycloaddition reactions with imines (i.e., the Castagnoli–Cushman Reaction (CCR)). Here, we disclose that a disulfide-embedded anhydride (i.e., dithiodiglycolic anhydride) unexpectedly underwent an efficient formal cycloaddition with aryl aldimines to afford functionalized 4-thiazolidinones, without complications arising from the CCR. Importantly, when 1,3-azadienes were employed, the 2-alkenyl-4-thiazolidinones were obtained without complications stemming from the sulfa-Michael reaction or the Tamura reaction. These 4-thiazolidinones constitute the core of several pharmaceuticals that display a broad spectrum of biological activities, including anti-HIV and anticancer. The current tactic obviates the need for thioglycolic acid, an alternative annulation partner associated with a strongly unpleasant odor. The ensuing N,S-heterocycles are then engaged in several selective fragment growth processes, including oxidation to sulfoxides, sulfones, and epoxysulfones. [ABSTRACT FROM AUTHOR]

Pyridazine is a significant skeleton that widely exists in drugs and bioactive molecules. We herein describe expeditious approaches to access polysubstituted pyridazines from readily accessible unactivated ketones and acylhydrazones via Cu-promoted C(sp3)–C(sp3) coupling/cyclization sequences in a single-step fashion. Notably, the disparate 3,4,6-trisubstituted pyridazines and 3,5-disubstituted pyridazines could be obtained by tailoring the ketone's structure and reaction conditions. These transformations feature good functional group compatibility, excellent step-economy, and chemoselectivity. The potential synthetic utility of these conversions is illustrated by scale-up reactions and late-stage derivatizations of the as-prepared pyridazine products. [ABSTRACT FROM AUTHOR]

An efficient one-pot pseudo three component cascade annulation reaction has been devised to generate the fluorescent β-carboline tethered imidazopyrido[3,4-b]indole derivatives. These scaffolds were afforded in high yields via one-pot cascade reaction of diversified β-carboline acetals with NH4Cl through the formation of three C–N bonds in a single operation. The current protocol is step-economical and offers high atom-economy, short reaction time and high structural diversity with excellent yields (57–90%). The synthesized compounds displayed promising photophysical properties and delivered luminescence quantum yield (ΦF) up to 55%. [ABSTRACT FROM AUTHOR]

C–H activation provides a straightforward approach to construct new chemical bonds and privileged heterocycles. However, due to common deficiencies, C–H activation still faces a great challenge towards sustainability and applications. Described herein is a robust and convenient rhodium-catalyzed regioselective C–H activation/[4 + 2] annulation for the synthesis of isoquinolones with salient features including a recyclable catalytic reaction system, unique regioselectivity, gram-scale synthesis with low catalyst loading (e.g., 0.5 mol%), ethanol as the green solvent, air and water compatibility, and simple purification processes. The roles of the hydroxy group and the pivaloyl part in both substrates, the additional pivotal function of propargyl alcohol partners, and the origin of the unique chemoselectivity are clarified based on integrated experimental and DFT studies. Additionally, a propargyl alcohol-connected distinctive hydrogen bonding network with the hydroxy group and the pivaloyl part is also rationally deduced for conferring the observed reverse regioselectivity by subsequent IGMH analysis. [ABSTRACT FROM AUTHOR]