The photolytic reaction of chromium-alkoxycarbene complexes with valine-derived, optically active thiazolines produced optically active@-lactam penam derivatives in fair to good yield and with high diastereoselectivity. In most cases alcoholosis of the &lactam followed by solvolysis of the thiazolidine ring produced optically active quaternary centers having carbon substituents in four different oxidation states-alkane, alkoxy, aldehyde, and ester. The ...