Studies On The Reduction Of Ketones By N-heterocyclic Carbene Boranes

N-heterocyclic carbene boranes(NHC-boranes or NHC-BH₃)have developed rapidly in organic chemistry.They do not exhibit“borane chemistry”,but instead they are proved 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.Because of N-heterocyclic carbenes boranes have good organometallic catalytic and organic catalytic properties.They have played an important role in organic synthesis over the past decades.However,little attention has been paid to the N-heterocyclic carbenes before Robinso's first synthesis of azacyclo-carbene-boranes.This thesis provides comprehensive coverage of the synthesis,characterization,and reactions of NHC-boranes.In 2012,Curran reported the reduction of aldimines by NHC-BH₃ and revealed NHC-BH₃ to be good hydride donors.Using NHC-BH₃,aldehydes could transfered to the corresponding alcohols in quite good yields even with silica gel.Very recently,our previous work demonstrated asymmetric reduction of tert-butanesulfinyl ketimines by NHC-BH₃ based on a triazole core in the presence of TsOH.Up to 95%yield and up to>99%diastereomeric excess were achieved.Based on this,we further studied the catalytic activity of various NHC-BH₃ and various acid-catalyzed ketones.We found an efficient method for the reduction of ketones via NHC-BH₃ mediated by FeCl_3.A wide range of ketones could smoothly proceed in the reduction and could give the corresponding alcohols in good to excellent yields,which made NHC-BH₃ a valuable alternative reductive reagent.