Oxazaborolidine catalysed enantioselective reduction of cyclic meso-imides

Abstract Full details of the enantioselective reduction of cyclic meso -imides catalysed by an enantiopure oxazaborolidine derived from ( S )- α , α -diphenylprolinol are reported. Treatment of the imides with borane in the presence of the catalyst led to a mixture of cis - and trans -hydroxylactams and, after subsequent ethanolysis, to the corresponding diastereomerically pure trans -ethoxylactams. The enantiomeric excesses were shown to be 68–94% by HPLC-determination. One example, in which the ethoxylactam was converted into the benzenesulfonyllactam, could be crystallized to >99% enantiomeric purity.