MODULATING STERIC EFFECTS IN DIASTEREOSELECTIVE STAUDINGER REACTION -SYNTHESIS OF OPTICALLY PURE CIS-BETA-LACTAMS

Diastereoselection in the synthesis of beta-lactams (14 and 15) via ke tene-imine cycloaddition (Staudinger reaction) using different chiral auxiliaries has been examined. While sterically demanding imines deriv ed from bicyclic aldehyde (1) with a beta chiral centre provided excel lent selectivity, use of imines derived from bicyclic aldehyde (17) wi th a gamma chiral centre was not effective. Improvement of stereoselec tivity was also sought using imines (6 and 7) derived from chiral amin es (2d,e) and chiral aldehyde (1). The bicyclic terpenoid skeleton of the chiral auxiliary in 1 was dismantled by ruthenium tetroxide oxidat ion to give multiply functionalized beta-lactams 23a-d in good yield.