Asymmetric addition of methyl nitroacetate to crotonaldehyde catalyzed by chiral amines

The asymmetric Michael addition of methyl nitroacetate to crotonaldehyde catalyzed by chiral amines was carried out. The maximum chemical yield of diastereomeric products amounted to 95 %. The best asymmetric induction (42 % e.e.) was achieved in the case of catalysis by (S)-prolinol. The diastereomeric mixture was converted to a mixture of stereoisomeric 3-methyl-2-methoxycarbonylpyrrolidines. Absolute configurations of (2S,3S)-and (2R,3S)-isomers formed in excess were determined using GLC by comparison with authentic samples of racemic and optically pure forms of 3-methylproline.