REGIOSELECTIVE AND STEREOSELECTIVE REDUCTION OF BICYCLIC IMIDES FOR THE ASYMMETRIC-SYNTHESIS OF HIGHLY SUBSTITUTED PYRROLIDINES

1,3-dipolar cycloaddition of N-phenylmaleimide with azomethine ylides generated from alpha-aminonitrile or alpha-aminoester oxazolidines gave bicyclic imides, which were reduced regio- and stereoselectively to hydroxylactams. In the aminonitrile series, reduction with NaBH4\CeCl3 at low temperature gave a single hydroxylactam in high yield. In the aminoester series the regioselectivity was more dependent on the structure, and other conditions (LiBEt3H) were found to obtain a single hydroxylactam which corresponds to a reverse regiochemistry when compared with the aminonitrile series.