Asymmetric Reduction Of Tert-butanesulfinyl Ketimines By N-heterocyclic Carbene Boranes

Boranes are widely used Lewis acids and N-heterocyclic carbenes(NHCs)are popular Lewis bases,The combination of an N-heterocyclic carbene(NHC)with a borane typically results in a complex called an N-heterocyclic carbene borane(or NHC-borane,for short).These complexes are formally analogous to many other Lewis acid/Lewis base complexes with boranes,but are in practice very different.NHC-boranes are tetravalent,neutral complexes that are not at all like trivalent,neutral boranes,and have only a passing resemblance to tetravalent,anionic borates.NHC-boranes are typically readily accessible and many are so stable that they can be treated like organic compounds rather than complexes.They do not exhibit ?borane chemistry?,but instead are proving to have a rich chemistry of their own as reactants,as reagents,as initiators,and as catalysts.They have significant potential for use in organic synthesis and in polymer chemistry.They can be used to easily make unusual complexes with a broad spectrum of functional groups not usually seen in organoboron chemistry.Many of their reactions occur through new classes of reactive intermediates including borenium cations,boryl radicals,and even boryl anions.This thesis provides comprehensive coverage of the synthesis,characterization,and reactions of NHC-boranes.In addition,NHC-boranes(NHC-BH3)were proven to be good hydride donors by Curran.The reduction of aldimines could proceedsmoothly in the presence of acetic acid,which could afford the corresponding achiral primary amines.However,chiral ?-branched amines,which often can be obtained by reduction of ketimines,are more valuable in organic synthesis,as they could be used as resolving agents and a key chiral source of important natural products and biologically active compounds.Normally,the involved reduction process has been reported using hydrogenation,metallic hydrides,hydrosilylation,transfer hydrogenation,etc.However,to the best of our knowledge,there are no reports related to the reduction of less active ketimines using NHC-BH3.Among the different methods for the reduction of ketimines,NHC-BH3 presents several advantages such as easy preparation,stability to air or water,avoidance of hazardous chemicals(metallic hydrides or H2),etc.Consequently,we herein demonstrate reduction of ketimines by NHC-BH3 using the well-known chiral auxiliary tert-butanesulfinyl group to induce the chirality to achieve asymmetric readuction.