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The atom-efficient formation of amide bonds has emerged as a top-priority research field in organic synthesis, as amide bonds constitute the backbones of proteins and represent an important structural motif in drug molecules. Currently, the increasing demand for novel discoveries in this field has focused substantial attention on this challenging subject. Herein, the degradable 1,3,5-triazo-2,4,6-triphosphorine (TAP) motif is presented as a new condensation system for the dehydrative formation of amide bonds between diverse combinations of aromatic carboxylic acids and amines. The underlying reaction mechanism was investigated, and potential catalyst intermediates were characterized using 31P NMR spectroscopy and ESI mass spectrometry.

Tetrakis(dimethylamido)diboron and tetrahydroxydiboron are herein reported as new catalysts for the synthesis of aryl amides by catalytic condensation of aromatic carboxylic acids with amines. The developed protocol is both simple and highly efficient over a broad range of substrates. This method thus represents an attractive approach for the use of diboron catalysts in the synthesis of amides without having to resort to stoichiometric or additional dehydrating agents., ファイル公開：2019-08-03

Amines are important building blocks possessing various applications in agrochemicals, the fine chemical industry, pharmaceuticals, materials science and biotechnology. The catalytic hydrogenation of nitriles is an important reaction for the one-step synthesis of diverse amines. However, significant amounts of side product formation during the course of the reaction is a major issue. In recent years, an enormous amount of work has been reported using both homogeneous and heterogeneous transition metal complex catalysts for the selective reduction of nitriles. Transition metal catalysts are the most crucial factor that controls the selectivity in this reaction. Therefore, transition metal catalysts are the central point of this review. We have also briefly discussed the effect of reaction parameters, selectivity to different substrate structures and reaction mechanisms. This review provides an overview of recent developments in transition metal-catalyzed nitrile reduction along with examples which highlight its vast potential in organic transformations.

Visible light sensitization of benzoyl azides was examined in reaction with N-phenylmethacrylamides to afford biologically important oxindoles and spirooxindoles via a cascade cyclization under mild reaction conditions. Mechanistic studies suggested a non-nitrene pathway, where triplet benzoyl azides act as the reactive intermediate.

A highly efficient ligand free catalytic system was developed for chemoselective transfer hydrogenation of α,β-unsaturated carbonyl compounds by palladium nanoparticles (PdNPs) in an aqueous reaction medium. The developed methodology offers chemoselective 1,4-reduction of various α,β-unsaturated carbonyl compounds such as carbonyls, amides, esters and nitriles with excellent chemoselectivity and effective catalyst recyclability.

A highly efficient polymer supported palladium-N–heterocyclic carbene (PS-Pd–NHC) catalytic system has been developed for direct reductive amination (DRA) of carbonyl compounds with primary/secondary amines in aqueous reaction medium. This new catalytic system represents a heterogeneous, recyclable and environmentally benign protocol. The developed methodology describes a simple one step approach for the synthesis of a wide variety of substituted amines exhibiting remarkable activity with excellent yield of a desired product. Furthermore, the catalyst was effectively recycled for six consecutive cycles without any significant loss in its catalytic activity.

The application of palladium on carbon (Pd/C) as a heterogeneous recyclable catalyst was investigated for the double carbonylation of o-dihaloarenes with amines providing excellent yield of N-substituted phthalimides in shorter reaction time as compared to earlier reported homogeneous protocols. Furthermore, the scope of the developed protocol was applied for the synthesis N-substituted phthalimides from o-halobenzoates and o-halobenzoic acid via a single step carbonylative cyclization reaction. The developed methodology describes an efficient one-step approach for the synthesis of an important class of heterocycles and tolerates a wide variety of functional groups. It circumvents the use of phosphine ligands with an additional advantage of catalyst recyclability for up to eight consecutive cycles.

Polymer supported diol functionalized ionic liquids (PS-DFILXs) were investigated as an efficient, heterogeneous and recyclable catalyst for coupling of carbon dioxide (CO2) to aziridines providing high conversion with excellent regioselectivity towards 5-aryl-2-oxazolidinones under mild and solvent free conditions. The developed methodology was found to be applicable for wide variety of 1-alkyl-2-arylaziridines producing the corresponding 5-aryl-2-oxazolidinones with good yields and excellent regioselectivity. The hydroxyl groups present on vicinal carbon of PS-DFILX proved crucial for higher efficiency of catalyst. In addition, the catalyst could be reused for four consecutive recycles without significant loss in its catalytic activity and selectivity. Hence, the developed process represents environmentally benign chemical fixation pathway of CO2 for synthesis of 5-aryl-2-oxazolidinones under mild condition.

Polyethylene glycol functionalized phosphonium salt (Br−Ph3+PPEG600P+Ph3Br−) was found to be an efficient, homogenous, recyclable catalyst for coupling of CO2 with a variety of aziridines producing corresponding 5-aryl-2-oxazolidinones with good yields and excellent regioselectivity under relatively mild and solvent free conditions. Furthermore, the catalyst was effectively recycled for four consecutive cycles without any significant loss in its catalytic activity and selectivity.

Amines are important building blocks possessing various applications in agrochemicals, the fine chemical industry, pharmaceuticals, materials science and biotechnology. The catalytic hydrogenation of nitriles is an important reaction for the one-step synthesis of diverse amines. However, significant amounts of side product formation during the course of the reaction is a major issue. In recent years, an enormous amount of work has been reported using both homogeneous and heterogeneous transition metal complex catalysts for the selective reduction of nitriles. Transition metal catalysts are the most crucial factor that controls the selectivity in this reaction. Therefore, transition metal catalysts are the central point of this review. We have also briefly discussed the effect of reaction parameters, selectivity to different substrate structures and reaction mechanisms. This review provides an overview of recent developments in transition metal-catalyzed nitrile reduction along with examples which highlight its vast potential in organic transformations.

A visible-light-mediated procedure for the unprecedented trifluoromethylchlorosulfonylation of unactivated alkenes is presented. It uses [Cu(dap)2]Cl as catalyst, and contrasts with [Ru(bpy)3]Cl2, [Ir(ppy)2(dtbbpy)]PF6, or eosin Y that exclusively give rise to trifluoromethylchlorination of the same alkenes. It is assumed that [Cu(dap)2]Cl plays a dual role, that is, acting both as an electron transfer reagent as well as coordinating the reactants in the bond forming processes.

A highly efficient ligand free catalytic system was developed for chemoselective transfer hydrogenation of α,β-unsaturated carbonyl compounds by palladium nanoparticles (PdNPs) in an aqueous reaction medium. The developed methodology offers chemoselective 1,4-reduction of various α,β-unsaturated carbonyl compounds such as carbonyls, amides, esters and nitriles with excellent chemoselectivity and effective catalyst recyclability.

PPN is effectively recovered for 6 consecutive cycles without any significant loss in activity.

Double carbonylation of o-diiodobenzene (I) in the presence of aromatic and aliphatic amines proceeds readily in the presence of Pd—C catalyst to afford phthalimides (IV) and (VI) in high to excellent yields.

A complete green and convenient strategy for the chemoselective transfer hydrogenation of various α,β-unsaturated carbonyl compounds using HCOONa as hydrogen source and a polymer-supported Pd-NHC catalyst system is given.

An highly efficient PS-Pd-NHC catalytic system has been developed for chemoselective conjugate reduction of α,β-unsaturated carbonyl compounds providing good to excellent conversion with remarkable chemoselectivity (up to 100%). The developed protocol is more advantageous due to use of HCOONa as hydrogen source, environmentally benign water as solvent and effective catalyst recyclability.