THE SYNTHESIS OF ARACEMIC 4-SUBSTITUTED PYRROLIDINONES AND 3-SUBSTITUTED PYRROLIDINES - AN ASYMMETRIC-SYNTHESIS OF (-)-ROLIPRAM

Conjugate additions of RCuCNLi to the chiral alpha,beta-unsaturated lactam 4 gives almost exclusive exo addition-a reversal in stereochemistry when cuprates were added to chiral lactam 1. The lactams 5 were transformed into 4-substituted pyrrolidinones 8 via a three-step sequence which involved decarbalkoxylation, silane reduction and metal-ammonia benzylamine cleavage. The chemical yields as well as the enantiomeric purity were very high for this process. As an example of the usefulness of this scheme, the antidepressant (-)-Rolipram was prepared in good overall yield. Furthermore, the bicyclic lactams 6 were readily transformed, using alane as the reducing agent, to 3-substituted pyrrolidines 11. Absolute configurations of 8 and 11 were confirmed by comparison with literature assignments which also gave strong support to the facial addition of the cuprates to 4.