The reduction of (5S)-5-alkyl-2, 4-dioxopyrrolidines, so-called tetramic acids, by NaBH4 gives only partial diastereofacial selectivity in the case of the N-substituted analogues 9f-i, unlike the carbamate derivatives 9a-e which give the reduced cis-pyrrolidinones 1OBa-e. Increasing the steric hindrance of either the N-or C-5-substituents enhances the re-face selectivity. On the other hand, reduction of the heterobicyclic compound 9n leads to a ...
