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Efficient heterogeneous catalysts for chemoselective hydrogenation of terminal and disubstituted alkynes and alkynols to monoenes based on Pd–P particles have been proposed. The influence of a zeolite support (Na-ZSM-5, MSM-41) and a phosphorus modifier on the properties of palladium catalysts in the semihydrogenation of acetylenic compounds is considered. Promotion with phosphorus increases the activity of palladium catalysts in hydrogenation of various acetylenic compounds 2.5- to 30-fold without reducing the selectivity for monoenes. The high selectivity for monoenes is determined by both thermodynamic and kinetic factors. The possibility of changing the ratio of the rates of hydrogenation of triple and double bonds by varying the nature of the solvent and the structural order of the catalyst particles was demonstrated using hydrogenation of acetylenic alcohols as an example. [ABSTRACT FROM AUTHOR]

Bismuth(III) triflate-catalyzed [4+2]-annulation of cyclic N-sulfonyl ketimines (derived from saccharin) and alkynyl alcohols (4-pentyn-1-ols and 5-hexyn-1-ols) has been reported. This cascade annulation provides a diverse array of polycyclic spiro-and-fused N,O-ketals with excellent substrate scope, good isolated yields, and diastereoselectivities under mild reaction conditions. [ABSTRACT FROM AUTHOR]

A novel photocatalytic strategy was proposed for selectively reducing alkynols to corresponding alkenols under ambient temperature and pressure. Carbon nitride nanosheets with Pd nanoparticles as cocatalysts exhibit high alkynol conversion and alkenol selectivity, which potentially replaces the current thermocatalysis and electrocatalysis. [Display omitted] Selective hydrogenation of alkynols to alkenols is an essential process for producing fine and intermediate chemicals. Currently, thermocatalytic alkynol hydrogenation faces several challenges, e.g., the safety of high-pressure hydrogen (H 2) gas and the need for elevated temperature, and unavoidable side reactions, e.g., overhydrogenation. Here, a novel photocatalytic strategy is proposed for selectively reducing alkynols to alkenols with water as a hydrogen source under ambient temperature and pressure. Under the irradiation of simulated solar light, carbon nitride (C 3 N 4) nanosheets with palladium (Pd) nanoparticles as cocatalysts (Pd–C 3 N 4 NSs) exhibit a 2-methyl-3-butyn-2-ol (MBY) conversion of 98% and 2-methyl-3-buten-2-ol (MBE) selectivity of 95%, outperforming state-of-the-art thermocatalysts and electrocatalysts. After natural-sunlight irradiation (average light intensity of 25.13 mW cm−2) for 36 h, a MBY conversion of 98% and MBE selectivity of 92% was achieved in a large-scale photocatalytic system (2500 cm2). Experimental and theoretical investigations reveal that Pd cocatalysts on C 3 N 4 facilitate the adsorption and hydrogenation of MBY as well as the formation of active hydrogen species, which promote the selective semihydrogenation of alkynols. Moreover, the proposed strategy is applicable to various water-soluble alkynols. This work paves the way for photocatalytic strategies to replace thermocatalytic hydrogenation processes using pressurized hydrogen. [ABSTRACT FROM AUTHOR]

A wide variety of regioselectively substituted carbazole derivatives can be synthesized by the gold‐catalyzed cyclization of alkynols bearing an indol‐3‐yl and an additional group at the homopropargylic positions. The regioselectivity of the process can be controlled by both the oxidation state of the gold catalyst and the electronic nature of the substituents of the alkynol moiety. The 1,2‐alkyl migration in the spiroindoleninium intermediate, generated after indole attack to the activated alkyne, is favored with gold(I) complexes and for electron‐rich aromatic substituents at the homopropargylic position, whereas the 1,2‐alkenyl shift is preferred when using gold(III) salts and for alkyl or non‐electron‐rich aromatic groups. [ABSTRACT FROM AUTHOR]

Annulations of unsaturated systems through C–H activation represent a powerful tool for producing multicyclic scaffolds. Having coordinating centers in both annulation partners (a dual coordination strategy) would afford remarkable selectivities in the outcomes. Along this concept, we report herein a Pd-catalyzed regioselective rollover cascade dual C–H annulation of o-arylphenols with alkynols for constructing phenanthrene scaffolds. Control, KIE and deuteration studies were conducted to determine the reaction mechanism, and downstream transformations and scaled-up reactions were carried out to assess the robustness of the transformation. [ABSTRACT FROM AUTHOR]

Herein, the PdII‐catalyzed construction of functionalized dihaloalkenynes from haloalkynes via a self‐haloalkynylation reaction, without specialized ligands or oxidizing additives, is reported. The method tolerates a diverse range of haloalkynes, including electron‐donating and electron‐withdrawing functional groups, such as macrocyclic alkynols, spiro‐oxy ring alkynols, and even carbazole‐containing, pyrrolidine‐2,5‐dione‐containing and silyl‐protected bromoalkynes. Using an opposite lithium halide (LiX) to the haloalkyne starting material, remarkably high regio‐ and stereoselectivity of the haloalkynylation reaction is possible, yielding 1‐bromo‐2‐chloroalkenyne or 2‐bromo‐1‐chloroalkenyne products as desired. [ABSTRACT FROM AUTHOR]

Palladium catalysts were obtained by the adsorption method involving the sequential deposition of polyvinylpyrrolidone (PVP) and then palladium ions on a modified zinc oxide surface without high-temperature calcination and reduction stages. The immobilized PVP-palladium catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), infrared spectroscopy (IRS), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and elemental analysis methods. It was found that the introduction of polymer into the catalyst's composition promotes the dispersion and uniform distribution of active phase nanoparticles (PdO, Pd0) on the surface of zinc oxide. The catalysts were tested in the hydrogenation of complex acetylene alcohol, 3,7,11-trimethyldodecyn-1-ol-3 (C15-yn) under mild conditions (0.1 MPa, 40 °C). For comparison, studies on stereoselective hydrogenation of the short-chain alcohol 2-hexynol-1 were performed. It was shown that modification of the catalyst with polymer improves its catalytic properties. High C15-alkenol selectivity (98%), activity (W = 70 × 10−6 mol/s), and stability (turnover number (TON) 62,000) were achieved on a Pd-PVP/ZnO catalyst. Varying the active phase made it possible to reduce the metal content without deteriorating the catalytic performance of the catalyst. [ABSTRACT FROM AUTHOR]

We studied the regularities of gas-chromatographic retention indices of aliphatic enyne alcohols containing С=С and С≡С bonds in the molecule (14 secondary and two tertiary homologues) on standard nonpolar polydimethylsiloxane stationary phases, which have not been characterized in sufficient detail earlier. Using homologous increments of retention indices iRI = RI – 100x, where х = int(M/14), М is the molecular weight number, and 14 is the mass number of the CH2 homological difference, one can compare data for structural analogs, including alkanols, alkenols, and alkynols. The features of comparing iRI values for compounds belonging to different homologous groups y ≡ M(mod14), for example, CnH2n+2O (y = 4), CnH2nO (y = 2), CnH2n–2O (y = 0), and CnH2n–4O (y = 12), are discussed. The main feature is that when the boundary value of y = 0 is passed, the relation between the parameter x and the number of carbon atoms in the molecule changes due to an increase in the formal unsaturation (the condition n = x – 1 is replaced by the condition n = x). Therefore, in the latter case, 100 should be subtracted from the iRI homologous increments to compare them with the data for structural analogs of other series. Taking this correction into account, we found that the iRI values for secondary enyne alcohols (12 ± 16) and previously characterized sec-alkynols (23 ± 21) virtually coincide, and for tertiary enyne alcohols, they are consistent with the data for all considered groups of structural analogues (alkanols, alkenols, and alkynols). [ABSTRACT FROM AUTHOR]

The catalytic partial hydrogenation of alkynols is a key approach for the synthesis of enols, which are crucial chemical intermediates for pharmaceuticals and essences. Low selectivity is the main challenge of the partial hydrogenation of alkynols due to the easy over-hydrogenation of alkynyl groups. Herein, ultrafine PdZn bimetallic nanoparticles (NPs) were anchored on a S-doped mesoporous carbon catalyst (PdZn/Meso_S-C) and used for the partial hydrogenation of alkynols. Zn metal with a high electron density was used to modify the active metal Pd to change the electronic and geometric configuration of the Pd active sites, which improve the selectivity of enols during the partial hydrogenation of alkynols. Furthermore, the use of a S-doped mesoporous carbon support dispersed and stabilized the ultrafine PdZn NPs due to strong interactions between the metal atoms and S sites. This also prevented PdZn ultrafine NPs from aggregating and increased the partial hydrogenation selectivity. The partial hydrogenation of propynol ethoxylate (PME) catalyzed by PdZn/Meso_S-C reached 96.0% enol selectivity, while the alkynol conversion reached 97.5%. The general applicability of PdZn/Meso_S-C for the partial hydrogenation of various alkynols has also been demonstrated. Thus, this work has great application prospects for the high-efficiency catalytic partial hydrogenation of alkynols. [Display omitted] • S-doped mesoporous carbon (Meso_S-C) was prepared and used as catalyst support. • PdZn ultrafine NPs were stably anchored on the Meso_S-C with high dispersion. • PdZn/Meso_S-C catalyst can partially hydrogenate of alkynols with high selectivity. • The general applicability and reusability of PdZn/Meso_S-C were also demonstrated. [ABSTRACT FROM AUTHOR]

The combination of organolithium chemistry with gold catalysis has enabled the development of a synthetic strategy for accessing polysubstituted indoles and carbazoles from readily available starting materials. This method is based on a "back‐to‐front" approach from ketopyrroles, generated by intramolecular carbolithiation of N,N‐bis‐(2‐lithioallyl)amines that evolve into 3,4‐bis(lithiomethyl)dihydropyrrole intermediates capable of reacting with carboxylic esters and Weinreb amides. These ketopyrroles have demonstrated to be excellent precursors of mono or bis(alkynols)pyrroles that, under gold‐catalysis, experience a benzannulation reaction providing access to regioselectively substituted indoles or carbazoles. [ABSTRACT FROM AUTHOR]

A mild and convenient method for the synthesis of 2,2-dihaloketones and gem -dihalolactols has been developed. For the synthesis of 2,2-dihaloketones, alkynes were employed as substrates to react with halogenating agents, Cl2 or ClBr, that were generated in situ from aqueous HCl and NCS or NBS, respectively. On the other hand, gem -dihalolactols could be prepared from alkynol substrates by using the same reaction conditions. This method could be applied to a broad range of substrates to give the corresponding products in low to good yields. [ABSTRACT FROM AUTHOR]

A new synthetic procedure for obtaining two previously reported donor-acceptor butadiene dyes, namely 5-(3,3-bis(4-methoxyphenyl)allylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione and 5-(3,3-bis(4-(dimethylamino)phenyl)allylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, based on the InCl3-catalyzed coupling 1,3-diethyl-2-thiobarbituric acid with 1,1-bis(4-methoxyphenyl)prop-2-yn-1-ol and 1,1-bis(4-(dimethylamino)phenyl)prop-2-yn-1-ol, respectively, is presented. The reactions, which cleanly proceed in water under MW irradiation, involve the initial generation of the corresponding enals by Meyer-Schuster rearrangement of the alkynols and their subsequent Knoevenagel condensation with the 2-thiobarbituric acid derivative. By following the same approach, the novel butadiene 5-(3,3-bi([1,1′-biphenyl]-4-yl)allylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, which was characterized by 1H and 13C{1H} NMR, IR, UV-Vis, elemental analysis and HRMS, was synthesized in 79% yield. [ABSTRACT FROM AUTHOR]

This work is addressing the selective hydrogenation of alkynols over hybrid catalysts containing Pd-nanoparticles, within newly synthesized hyper-cross-linked polystyrenes (HPS). Alkynols containing C5, C10, and C20 with a terminal triple bond, which are structural analogues or direct semi-products of fragrant substances and fat-soluble vitamins, have been studied. Selective hydrogenation was carried out in a batch mode (ambient hydrogen pressure, at 90 °C, in toluene solvent), using hybrid Pd catalysts with low metal content (less than 0.2 wt.%). The microporous and mesoporous HPS were both synthesized and used as supports in order to address the influence of porosity. Synthesized catalysts were shown to be active and selective: in the case of C5, hydrogenation selectivity to the target product was more than 95%, at close to complete alkynol conversion. Mesoporous catalysts have shown some advantages in hydrogenation of long-chain alkynols. [ABSTRACT FROM AUTHOR]

Pd catalysts are widely used in alkynol semi-hydrogenation. However, due to the existence of scaling relationships of adsorption energies between the key adsorbed species, the increase in conversion is frequently accompanied by side reactions, thereby reducing the selectivity to alkenols. We report that the simultaneous increase in alkenol selectivity and alkynol conversion is achieved by manipulating interstitial atoms including B, P, C, S and N in Pd catalysts. A negative linear relationship is observed between the activation entropies of 2-methyl-3-butyn-2-ol and 2-methyl-3-buten-2-ol which is highly related to the filling of d-orbital of Pd catalysts by the modification of p-block elements. A catalyst co-modified by B and C atoms has the maximum d charge of Pd that achieves a 17-fold increase in the turn-over frequency values compared to the Lindlar catalysts in the semi-hydrogenation of 2-methyl-3-butyn-2-ol. When the conversion is close to 100%, the selectivity can be as high as 95%. Circumventing the linear scaling relationship in the semi-hydrogenation is challenging. Here the authors report a method for breaking the scaling relationships using ordered mesoporous carbon-supported Pd nanocatalysts with d-electron gain by p-block atoms occupying interstitial sites in the lattice as a greener alternative to Lindlar catalysts for the selective hydrogenation of alkynols. [ABSTRACT FROM AUTHOR]

Polymer‐supported PdCu alloy nanoparticles with a palladium to copper atom ratio of 1 have been synthesized upon: (i) Coordination of palladium/copper acetate to 2,2'‐bipyridine‐end functionalized poly(lactic acid) (PLA); (ii) Stereocomplexation of PLA‐based macrocomplexes of opposite stereochemistry, and (iii) metal reduction with hydrogen. The obtained supported PdCu nanoparticles were successfully applied in the semi‐hydrogenation of industrially important alkynols, such as 3‐hexyn‐1‐ol and 2‐butyne‐1,4‐diol leading to the corresponding cis‐alkenol in high selectivity (98 %) under mild reaction conditions (i. e. ethanol, T (25 °C), p(H2)=3 bar) in the absence of any further additive. From a comparison of the catalytic performance of supported PdCu nanoparticles with those of Pd and Cu, located in the same chemical environment, emerged a clear alloy effect (i. e. high chemoselectivity for the alkene at high alkyne conversion). Recycling experiments conducted with the PdCu‐based catalyst proved the stability of the catalyst with time, even by its recovering in air atmosphere. [ABSTRACT FROM AUTHOR]

In this study, we discovered that α-bromocarboxamides react with alkynols containing tertiary alcohol moieties to produce congested ethers or heterocycles. Here, the etherification and hydroamidation reactions can be controlled by a suitable base. Both C–O and C–N bond formations occurred without a transition-metal catalyst. The stereospecific etherification and cyclization of diastereo-enriched α-bromocarboxamide afforded the corresponding diastereo-enriched ether and heterocyclic compound. [ABSTRACT FROM AUTHOR]

Most non-palladium catalysts employed in Sonogashira cross-coupling work at high temperatures of 120–140 °C and with well-defined ligands. Palladium-based catalysts with bulky and electron-rich phosphine ligands generally show the best performance for the above-mentioned cross-coupling procedure. Herein, we report a new protocol for Csp–Csp2 Sonogashira cross-coupling between a terminal alkyne and aryl halide using the cheap and commercially available catalyst CuSeO3·2H2O. The title reaction proceeds using a variety of terminal alkynes, affording diaryl or aryl–alkyl acetylenes in high yields under mild conditions in the absence of ligands. Alkyl acetylenes, ethynylsilanes, and alkynols are efficiently coupled with aryl iodides and aryl bromides. The mechanism of the reaction was evaluated using computational DFT studies. To the best of our knowledge, this is the first example of the use of an oxygen-bridged copper-based bimetallic catalyst for Csp–Csp2 Sonogashira cross-coupling reactions under mild conditions. The reaction is palladium-free up to a limit of 0.2 ppm. [ABSTRACT FROM AUTHOR]

Polarized alkynes such as ynol ethers and ynamides have attracted much attention due to their inherent unique reactivity. Herein, we report Au(I)-catalyzed hydroalkoxylation/Claisen rearrangement cascade reactions of aryl ynol ethers and ynamides with allylic alcohols. At the first stage (hydroalkoxylation) of this cascade reaction, attack of allylic alcohols to aryl ynol ethers or ynamides occurs at the α-position of the polarized alkynes in a completely regioselective manner. Claisen rearrangement of the resulting adducts subsequently takes place to give γ,δ-unsaturated esters or amides, respectively. The [Au(IPr)NTf2 ] catalyst is most effective for this reaction, and the reaction proceeds under mild conditions (in the case of aryl ynol ether: in THF, 60 °C; in the case of ynamides: in toluene, 80 °C) in an atom-economical way. [ABSTRACT FROM AUTHOR]

Designing highly active and stable lead-free palladium-based catalysts without introducing surfactants and stabilizers is vital for large-scale and high-efficiency manufacturing of cis-enols via continuous-flow semi-hydrogenation of alkynols. Herein, we report an intermetallic PdZn/ZnO catalyst, designed by using the coupling strategy of strong electrostatic adsorption and reactive metal-support interaction, which can be used as a credible alternative to the commercial PdAg/Al2O3 and Lindlar catalysts. Intermetallic PdZn nanoparticles with electron-poor active sites on a Pd/ZnO catalyst significantly boost the thermodynamic selectivity with respect to the mechanistic selectivity and therefore enhance the selectivity towards cis-enols. Based on in situ diffuse reflectance infrared Fourier-transform spectra as well as simulations, we identify that the preferential adsorption of alkynol over enol on PdZn nanoparticles suppresses the over-hydrogenation of enols. These results suggest the application of fine surface engineering technology in oxide-supported metal (particles) could tune the ensemble and ligand effects of metallic active sites and achieve directional hydrogenation in fine chemical synthesis. The semi-hydrogenation of alkynol to cis-enol is a critical process in the industrial production of fine and intermediate chemicals, but viable alternatives to lead-free palladium-based catalysts for this reaction are scarce. Here, an intermetallic PdZn/ZnO nanoparticle catalyst is designed and its reactivity described. [ABSTRACT FROM AUTHOR]

A protocol involving intramolecular formal [4+2]‐cycloaddition of in situ generated o‐aza‐quinone methide for the facile synthesis of 1,4‐heterocycle‐fused quinoline motifs is demonstrated. The cascade involved tandem C−O, C−C, and C−N bond formation and also exhibited excellent functional group tolerance. Enantiomerically enriched 1,4‐oxazepino quinolines were synthesized using alkynols derived from L‐amino acids. The sulfoxide embedded quinolines were transformed to pentacyclic 1,4‐thiepino tethered indeno‐quinoline scaffolds via Pummerer cyclization. [ABSTRACT FROM AUTHOR]

Reactions of Cp*OsCl(PPh3)2 (Cp* = pentamethylcyclopentadienyl) with alkynes and alkynols are described. Treatment of Cp*OsCl(PPh3)2 with phenylacetylene and trimethylsilylacetylene gave the vinylidene complexes Cp*OsCl(=C=CHPh)(PPh3) and Cp*OsCl(=C=CH2)(PPh3), respectively. Treatment of Cp*OsCl(PPh3)2 with the internal alkyne dimethyl acetylenedicarboxylate produced the η2-alkyne complex Cp*OsCl(η2-MeO2C≡CCO2Me)(PPh3). Treatment of Cp*OsCl(PPh3)2 with the propargylic alcohol HC≡CC(OH)Ph2 gave the osmium allenylidene complex Cp*OsCl(=C = C=CPh2)(PPh3). The outcomes of the reactions of Cp*OsCl(PPh3)2 with ω-alkynols HC≡C(CH2)nOH are dependent on the length of the -(CH2)n- linker. The reaction with 3-butyn-1-ol produced the cyclic oxycarbene complex Cp*OsCl{=C(CH2)3O}(PPh3) exclusively. The reactions with 4-pentyn-1-ol produced a mixture of the hydroxyalkyl vinylidene complex Cp*OsCl{=C=CH(CH2)3OH}(PPh3) and the cyclic oxycarbene complex Cp*OsCl{=C(CH2)4O}(PPh3) in about 10:1 molar ratio. The reaction with 5-hexyn-1-ol gave exclusively the hydroxyalkyl vinylidene complex Cp*OsCl{=C=CH(CH2)4OH}(PPh3). [ABSTRACT FROM AUTHOR]

A substrate dependent regio‐ and stereoselective domino hydroalkoxylation‐formal‐[4+2] cycloaddition is described for the facile synthesis of linear as well as spirocyclic 1,4‐heterocycle‐fused chromene ketals. Enantiospecific synthesis of oxazepino chromene derivatives was successfully carried out using chiral pool amino alkynols. The developed hydroalkoxylation cascade offered rapid access to the spirocyclic [6‐6‐7‐6] tetracyclic core of cytorhizhins B–D with correct relative configuration. [ABSTRACT FROM AUTHOR]

The first general and regioselective Pd‐catalyzed cyclocarbonylation to give α‐methylene‐β‐lactones is reported. Key to the success for this process is the use of a specific sterically demanding phosphine ligand based on N‐arylated imidazole (L11) in the presence of Pd(MeCN)2Cl2 as pre‐catalyst. A variety of easily available alkynols provide under additive‐free conditions the corresponding α‐methylene‐β‐lactones in moderate to good yields with excellent regio‐ and diastereoselectivity. The applicability of this novel methodology is showcased by the direct carbonylation of biologically active molecules including natural products. [ABSTRACT FROM AUTHOR]

The effect of the composition of the catalytic system and reaction conditions on the properties of phosphorus-modified palladium catalysts in hydrogenations of alkynols was studied. Modification with phosphorus increased the activity and turnover number of palladium catalysts in the hydrogenation of the model compound 2-methyl-3-butyn-2-ol (MBY) without any reduction in the selectivity to 2-methyl-3-butene-2-ol at 95–98% MBY conversion. The promoting effect of phosphorus on the properties of the palladium catalyst is caused not only by an increase in the particle size, but also, probably, by a change in the energy of interaction of reagents with the active sites. Hypotheses on the nature of the carriers of catalytic activity in Pd–P particles were discriminated using kinetic methods with the differential selectivity of catalytic systems as the main measured parameter under the conditions of competition between two alkynols. The hydrogenation of acetylenic alcohols involves only one of the two potentially active forms in Pd–P nanoparticles—Pd(0) clusters, whereas the hydrogenation of the resulting allyl alcohols involves both Pd(0) clusters and palladium phosphides. [ABSTRACT FROM AUTHOR]

This work reports gold‐catalyzed iminations of terminal propargyl alcohols with anthranils or isoxazoles to yield E‐configured α‐amino‐2‐en‐1‐ones and ‐1‐als with complete chemoselectivity. These catalytic iminations occur exclusively with C(1)‐nucleophilic additions on terminal alkynes, in contrast to a typical C(2)‐route. For 3,3‐dialkylprop‐1‐yn‐3‐ols, a methyl substituent is superior to long alkyl chains as the 1,2‐migration groups toward α‐imino gold carbenes. For secondary prop‐1‐yn‐3‐ols, phenyl, vinyl, and cyclopropyl substituents are better than hydrogen as the migrating groups, obviating typical gold carbene reactions. DFT calculations have been performed to rationalize the observed C(1)‐regioselectivity and the preferable cyclopropyl migration based on gold carbene pathways. [ABSTRACT FROM AUTHOR]

A practical and environmentally benign Brønsted acid−catalyzed protocol for the preparation of all-carbon tetrasubstituted allenes, consisting in the direct S N ˈ addition of tri- or dimethoxy arenes or allyltrimethylsilane to tertiary propargylic alcohols, has been developed. In addition, a straightforward synthesis of densely substituted 2 H -chromenes by metal-free tandem allenylation/heterocyclization reaction of methoxyphenols and tertiary alkynols is presented. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Magnesium and magnesium alloys have important applications in aviation, electronic devices, medical equipment, and automotive industries, while the corrosion is a common and real problem that must be solved for these applications. In this paper, a novel and effective anti-corrosive composite coating on AZ31 Mg alloys was prepared by the combination of micro-arc oxidation (MAO) layer, corrosion inhibitor and hydrophobic wax film technologies. And among these, the MAO treated micro- and nanopores as the container of corrosion inhibitor and the solid hydrophobic wax as the multifunctional sealing isolating agent. The morphology and phase composition of the resulting composite coatings were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively, indicating the successful synthesis of the organic-inorganic composite coating. The potentiodynamic polarization and electrochemical impedance spectroscopy measurements showed that compared with the MAO membrane covered Mg alloys, the organic-inorganic composite coating has superior corrosion resistance with the a lower corrosion current (5.764 × 10−9 A/cm2) and a higher protection efficiency (99.7%) after immersion in 3.5 wt% NaCl solution, attributing to the synergistic effect of effective inhibition of inhibitor and the physical barrier ability of hydrophobic film and MAO membrane. This simple and low cost strategy to fabricate organic-inorganic composite anticorrosion coatings would have promising applications in the corrosion protection of the light metals and their alloys. Highlights • In-situ growth of porous oxide coating as an inhibitor micro/nano-containers. • Synthesis of a new type of effective corrosion inhibitor with long alkyl chain. • Lower corrosion current density and high protection efficiency were obtained by the synergistic effect of hydrophobic film and porous oxide layer with alkynol inhibitor. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The intramolecular hydroalkoxylation of gem -difluorinated alkynols was found possible under Au catalysis. • The nature of the solvent was found to be especially critical in the cyclization of gem -difluorohomopropargylic alcohols. • In THF, gem -difluorohomopropargylic alcohols generated the corresponding 2,3-dihydrofurans. • In toluene, the 2,3-dihydrofurans produced underwent subsequent aromatization to the furan. Abstract The intramolecular hydroalkoxylation of gem -difluorinated alkynols was found possible under Au catalysis, allowing for the preparation of a series of fluorinated heterocycles. The nature of the solvent was found to be especially critical in the cyclization of gem -difluorohomopropargylic alcohols as it dictated whether the resulting 2,3-dihydrofuran underwent subsequent aromatization to the corresponding furan or not. [ABSTRACT FROM AUTHOR]

A novel palladium‐acid co‐catalyzed C(sp)−C(sp2) cleavage of alkynoates for the construction of dibenzo[c,h]xanthene derivatives is reported. A catalytic amount of triflic acid (TfOH) afforded an efficient transformation into the final product. Furthermore, a reduction process of alkynoates was observed during the formation of dibenzo[c,h]xanthene, preliminary mechanistic studies indicated that the protonation of the new‐formed methyl group in dibenzo[c,h]xanthene mainly came from water. [ABSTRACT FROM AUTHOR]

In this paper we outline how dihalohydration reactions of propargylic alcohols can be used to access a wide variety of useful halogenated building blocks. A novel procedure for dibromohydration of alkynes has been developed, and a selection of dichloro and dibromo diols and cyclic ethers were synthesized. The dihalohydration of homo‐propargylic alcohols provides a useful route to 3‐halofurans, which were shown to readily undergo cycloaddition reactions under mild conditions. Finally, a novel ring expansion of propargylic alcohols containing a cyclopropylalkyne provides access to halogenated alkenylcyclobutanes. [ABSTRACT FROM AUTHOR]

Here, we report the first divergent synthesis of benzo-fused O-heterocycles by p-toluene sulfonic acid promoted cascade reactions involving alkyne hydration, double cyclization, ring contraction and C–O bond cleavage from alkynols. The reaction mechanism was validated by obtaining the X-ray structure of fused benzo[b]oxepine intermediates. Moreover, some of the obtained derivatives could be transformed into 2,3-disubstituted naphthoquinones as important structural motifs in natural products and bioactive molecules. [ABSTRACT FROM AUTHOR]

A green methodology to synthesize 2-organoselanyl-naphthalenes based on the reaction of alkynols with diaryl diselenides is described. The electrophilic species of selenium were generated in situ, by the oxidative cleavage of the Se–Se bond of diaryl diselenides by Oxone® using water as the solvent. The reactions proceeded efficiently under ultrasonic irradiation as an alternative energy source, using a range of alkynols and diorganyl diselenides as starting materials. Through this methodology, the corresponding 2-organoselanyl-naphthalenes were obtained in moderate to good yields (56–94%) and in short reaction times (0.25–2.3 h). [ABSTRACT FROM AUTHOR]

A novel procedure for the synthesis of cyclohexanones from alkynol or enyne derivatives through a cationic cyclization has been developed. The key points to obtain the six-membered ring derivatives are the use of starting materials containing a terminal alkyne, the use of tetrafluoroboric acid as a promoter of the cationic cyclization, and the appropriate selection of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) as solvent. This strategy can be extended to the biomimetic cationic cyclization of several terpene-derived polyenynes. [ABSTRACT FROM AUTHOR]

Abstract: n‐Tetrabutylammonium organic salts were used for the first time as catalysts for the coupling of CO2 with 2‐methyl‐3‐butyn‐2‐ol to form an α‐methylene cyclic carbonate. Final yields up to 98 % were reached in less than 10 h at 353 K and 3 MPa under solvent‐free conditions. A particular synergistic effect between the cation and the anion of the organocatalyst was demonstrated through catalyst screening. Online kinetic studies by Attenuated Total Reflectance (ATR) IR spectroscopy correlated to DFT calculations revealed compelling evolution of solvation of the catalyst during the reaction that provided insight into the underlying reason for the observed unique kinetics and selectivity. Such in‐depth fundamental mechanistic and kinetic studies enabled determination and comprehension of the key parameters favoring the design of novel, highly active and selective catalysts for valorization of CO2 as a chemical feedstock. [ABSTRACT FROM AUTHOR]

Ag(I)- or Ag(I)–Au(I)-catalyzed cascade annulation of alkynols (5-hexyn-1-ol systems) with α-ketoesters involving a dual activation process (π and σ) has been developed for the first time. This reaction proceeds through cycloisomerization of alkynol to give the 6-endo-enol ether followed by annulation with an α-ketoester to furnish furo[2,3-b]pyran-2-ones in good yields. Chemical structures of all products were rigorously confirmed by single crystal X-ray analysis and analogy. [ABSTRACT FROM AUTHOR]

Abstract: Several new ruthenium complexes supported by the P,N‐donor ligand 8‐(diphenylphosphino)quinoline (DPPQ) were synthesized, including [RuCl2(DPPQ)2] (1), [Ru(μ‐Cl)(DPPQ)2]2(BPh4)2 (2), and [RuCl(DPPQ)2Py](BF4) (3). Complex 2, with only 1 mol % loading, was found to be catalytically active for the endo cycloisomerization of various terminal alkynols to endo‐cyclic enol ethers in moderate to excellent yields. In particular, the 7‐ and 8‐endo heterocyclization can be achieved efficiently to give the seven‐membered 3‐benzoxepine and eight‐membered 3‐benzo[d]oxocine derivatives. The stoichiometric reactions of 2 with various alkynol substrates have been carried out to investigate the mechanism, which led to a series of seven‐, six‐, and five‐membered oxacyclocarbene ruthenium complexes including [RuCl(DPPQ)2{=CCH2C6H4CH2CH2O}](BPh4) (12) and [RuCl(DPPQ)2{=CCH2(CH2)nCH2O}](BPh4) (n=3, 12′; n=2, 13; n=1, 14). The quantitative transformation of oxacyclocarbene 12 into catalyst 2 and 3‐benzoxepine 5 a as well as the efficient catalytic activity of 12 for the endo‐cyclization of 2‐(2‐ethynylphenyl)ethanol (4 a) demonstrated that 12 is a key intermediate involved in the catalytic cycle. Moreover, comparative studies on the modeling reactions and catalytic activity of the series of oxacyclocarbene complexes indicated that the different catalytic activity of 2 for the endo‐cycloisomerization of different types of alkynols can be related to the reactivity of the respective ruthenium oxacyclocarbene intermediates. [ABSTRACT FROM AUTHOR]

Homoisoflavonoids were formed in DMSO exclusively, and flavones were formed in t-AmOH when salicylaldehyde and alkynoic acids reacted with [Ru(p-cymene)Cl2]2 and CsOAc. They were formed through C-H activation of salicylaldehyde and decarboxylative coupling of alkynoic acid. This reaction system showed good yields, broad substrate scope, and good functional group tolerance. It was found that chalcone was an intermediate in the formation of both homoisoflavonoid and flavone. [ABSTRACT FROM AUTHOR]

Lewis acid mediated 5/6/7-endo-dig hydroalkoxylation-reduction cascade on internal alkynols gave an expedient, stereoselective synthesis of cyclic ethers and 1,4-oxazepanes. The strategy has been extended to the first examples of hydroalkoxylation-alkyne Prins-type cyclization cascade of alkyne-tethered alkynols, giving access to oxa-bicyclic scaffolds. This method was used as the key step in the stereoselective total synthesis of calyxolane A-B, as well as (±)-centrolobine and its homologue. [ABSTRACT FROM AUTHOR]

Metallacycloallenes are metallacyclic derivatives of cyclic allenes, in which a CH2 (type A) or CH (type B) segment is formally replaced by an isolobal transition-metal fragment. In constrast to the well-developed chemistry of metallacycloallenes of type A, the synthesis of metallacycloallenes with the structural features of type B has met with limited success. In this study, we present the reaction of η2-alkynol-coordinated osmacycle 1 with 2-aminopyridine in the presence of hypervalent iodine reagent, leading to the formation of imidazopyridinium-fused 4-osmacyclohexa-2,3,5-trienone 2 and 4-osmacyclohexa-2,5-dienone 3. Two key intermediates, η2-ethynyl ketone coordinated osmacycle 4 and 4-osmacyclohexa-2,5-dienone 5, were isolated and fully characterized, which suggest the hypervalent iodine reagent plays an important role in the formation of the fused metallacycloallene 2. [ABSTRACT FROM AUTHOR]

The previously unexplored metal-catalyzed [5 + 2] cycloadditions of vinylcyclopropanes (VCPs) and electron-rich alkynes (ynol ethers) have been found to provide a highly efficient, direct route to dioxygenated seven-membered rings, a common feature of numerous natural and non-natural targets and building blocks for synthesis. The reactions proceed in high yield at room temperature and tolerate a broad range of functionalities. Substituted VCPs were found to react with high regioselectivity. [ABSTRACT FROM AUTHOR]

Gold(III)-catalyzed cycloisomerization of α-bis(indol-3-yl)methyl alkynols selectively affords 1-(indol-3-yl)carbazoles, in a transformation that takes place through a selective 1,2-alkyl vs 1,2-vinyl migration step in the vinyl-gold intermediate generated from the initial 5-endo-spirocyclization. The reaction proceeds well with either tertiary or secondary starting alkynols as well as with a wide variety of alkyne substituents. The key role of the other indol-3-yl substituent for the unexpected selectivity in the 1,2 rearrangement has also been supported by DFT calculations that reveal a low barrier, two-step mechanism in the alkyl migration path where the second indole significantly stabilizes a carbocationic intermediate. [ABSTRACT FROM AUTHOR]

A novel cascade reaction of internal alkynols with 1-(2-aminophenyl)prop-2-ynols has been developed to form a new N,O-containing fused 5,5,6-tricyclic skeleton. Mechanistic studies indicate that this reaction proceeds via alkynol cycloisomerization, intermolecular substitution with 1-(2-aminophenyl)prop-2-ynols, and intermolecular addition with alkynols and consequent cyclizations. In this way, two C–C bonds, one C–O bond and one C–N bond form to give a tricyclic skeleton in a single reaction. [ABSTRACT FROM AUTHOR]

A novel Lewis acid catalyzed intermolecular cascade annulation of alkynols with α-ketoesters has been developed. This simple and efficient cascade annulation proceeds through a 5-exo-dig cyclization of alkynols followed by annulation with α-ketoester to provide a wide variety of unsaturated γ-spiroketal-γ-lactones (1,6-dioxaspiro[4.4]non-3-en-2-ones) related to many natural products. [ABSTRACT FROM AUTHOR]

This work highlights a novel hybrid catalyst, intermetallic PdZn on CN@ZnO (PdZn/CN@ZnO), which serves as a highly efficient heterogeneous catalyst for semihydrogenation of 2-methyl-3-butyn-2-ol utilizing water as the solvent. Compared with intermetallic PdZn on ZnO (PdZn/ZnO), PdZn/CN@ZnO displays almost sixfold higher TOF while retaining high selectivity. It is assumed that the introduction of biomass-derived hydrophilic nitrogen-doped carbon into the ZnO helped to promote catalyst dispersion in aqueous media, ensuring better mass transfer. Further experiments and theoretical calculations showed that from Pd particles to intermetallic PdZn, the decrease of corner and edge Pd atoms might be a factor leading to the improvement of selectivity. Recycling experiments demonstrated that the PdZn/CN@ZnO catalyst could be reused at least eight times without significant decrease in activity or selectivity. Furthermore, when applied to industrially relevant alkenols that are building molecules for the production of vitamin E, the present catalyst still offered excellent performance. It is expected that the present catalytic system will demonstrate its high potential for practical production of vitamin E. [ABSTRACT FROM AUTHOR]

An unexpected PtCl4-catalyzed cyclization reaction of tertiary indol-2-yl-3-alkynols occurred smoothly in toluene to form various poly-substituted carbazole derivatives efficiently. A possible mechanism involving the formation of a spiro-tricyclic intermediate via indole C-2 attack, highly selective ring expansion and then 1,2-migration has been proposed for the formation of carbazoles. [ABSTRACT FROM AUTHOR]

A Lewis acid-mediated cascade annulation of o-alkoxy alkynols in the presence of ZnBr2 has been developed. The cascade cyclization proceeds through a 5-exo-dig cyclization followed by a Friedel-Crafts reaction and ring-opening sequence to synthesize indeno[1,2-c]chromenes. This protocol provides a broad substrate scope in moderate to good yields with high regioselectivity. The reaction with benzo-fused cycloalkyl ketones gave an unexpected alkyne C-C bond cleavage resulting in fused polycycles. [ABSTRACT FROM AUTHOR]

[Display omitted] Herein, we report a Bi(OTf) 3 -catalyzed cascade condensation between alkynols (particularly pent-4-yn-1-ols and hex-5-yn-1-ols) and terminal alkynes (aryl alkynes) to facile access to diverse propargyl cyclic ethers (2‑alkynyl tetrahydrofurans and 2‑alkynyl tetrahydropyrans). This simple and efficient cascade transformation proceeds through initial intramolecular hydroalkoxylation of alkynols to give corresponding cyclic enol ethers (via exo -dig or endo -dig mode of ring-closure) followed by hydroalkynylation. Cost-effective, naturally abundant, green Lewis acid catalysis, ambient reaction conditions, short reaction times, good substrate scope, and high yields are salient features of this strategy. [ABSTRACT FROM AUTHOR]

DFT calculations have been carried out to study the detailed mechanisms of the carboxylative cyclization reaction between propargylic alcohols and CO2 catalyzed by N-Heterocyclic Olefins (NHO), as well as the molecular orbital theory. Results indicated that this type of reaction prefers a three steps mechanism controlled by free NHO rather than to be catalyzed by the NHO-CO2 adducts. For the first step, CO2 promotes the hydrogen transfer from alkynol to NHO to form the carboxylate, in which propargylic alcohols was deprotonated by the free NHO acted as the catalyst precursor to form the alkynol anion; meanwhile, alkynol anion captures carbon dioxide to form the carboxylate. We found this CO2 promoting Hydrogen abstraction mechanism would decrease the reaction energy barrier and increase releasing heat of this reaction. Secondly, a five-membered-ring intermediate is easily formed to generate carboxylate via an intramolecular ring-closing reaction. Finally, the production generated through a protonating process. [ABSTRACT FROM AUTHOR]