CHIRAL PHOSPHINAMIDES - NEW CATALYSTS FOR THE ASYMMETRIC REDUCTION OFKETONES BY BORANE

We have identified a new class of catalysts for the asymmetric reducti on of prochiral ketones by borane. Key to the architecture of effectiv e catalysts is an N-P=O structural unit which may be part of a phosphi namide, phosphonamide or a related structure, Such catalysts are simpl e to prepare, are often crystalline solids and may be recovered from r eduction reactions and reused. The catalysts act essentially as Lewis bases, serving to increase the reactivity of borane by electron donati on. The incorporation of a hydroxy group into the catalyst provides an adjacent Lewis acid site upon reaction with borane and thus affords a superior catalyst capable of asymmetric inductions of up to 92% ee.