Asymmetric Cascade Reactions With Transition Metals And Organocatalyst

Multi-catalyst combined catalysis refers to that two or more individual catalysts work together to catalyze a reaction in concert manner.Such a strategy integrates the catalytic activity of all catalysts to enable the transformations that are difficult to complete with a single catalyst.The organo-metal combined catalysis is able to greatly expand the scope of substrates and provides more opportunities to control the stereoselectivity.We have developed a highly chemo-,regio-,and enantioselective hydroaminomethylation of olefins by employing a rhodium catalyst with a commercial ligand and a phosphoric acid catalyst.The relay catalytic reaction consists of a rhodium-catalyzed hydroformylation step and Bronsted acid catalyzed subsequent dynamic kinetic reductive amination process.The salient features of this reaction include mild conditions(1 bar of syngas,room temperature in most cases),high yields,and high enantioselectivities.Besides styrenes,other olefins,including aliphatic alkenes,acrylamides,and vinyl esters can also undergo this transformation.Here,we show that a multi-catalyst system consisting of a rhodium(1)complex,a palladium(0)complex,a chiral Bronsted acid catalyst,and an achiral amine works ideally to promote a cascade hydroformylation and asymmetric allylation reaction.This method enables the transformation of readily available styrenes,allylic alcohols,and syngas to a-quaternary chiral aldehydes with high yields and enantioselectivities under mild conditions.We have developed an asymmetric Wolff rearrangement reaction that directly transforms α-diazoketones into chiral esters using a commercially available phenol derivatives.The cascade reaction consists of a Wolff rearrangement reaction driven by visible light,which slowly generates the ketene intermediate,and subsequent asymmetric ketene esterification catalyzed by chiral benzotetramisole.The method represents another effective access to the broadly useful α,α-disubstituted carboxylic esters.