Diastereomerically pure pyrrolidin-2-ones by intramolecular Michael reaction. Synthesis of both (S)- and (R)-3-pyrrolidineacetic acid

By intramolecular conjugate addition of their derived enolates, the amides 5 and 6 gave diastereomeric mixtures of pyrrolidin-2-ones 10,11 and 12,13 , in good yield and 80:20 d.r. After chromatographic separation, the configuration of pure diastereomers was assigned from 1 H NMR data. The usefulness of this intramolecular cyclisation was proven by conversion of either 10 or 12 into pyrrolidin-2-one 14 which through simple steps gave ( S )-3-pyrrolidineacetic acid, 2 . Following the same synthetic scheme, but starting from either 11 or 13 , ( R )-3-pyrrolidineacetic acid 3 was obtained. The major isomer can be converted into ( S )-3-pyrrolidincacetic acid