One-pot synthesis of (3R)-hydroxy-beta-lactams via enolates of 2-tert-butyl-1,3-dioxolan-4-ones .1.

Seebach's synthetic method of self-regeneration of stereocenters ''SRS'' has been applied to the addition reaction of diphenylimine 1 to the lithium enolates of (2S,5S)-2-(tert-butyl)-5-methyl-1,3-dioxolan-4-one 2a and of (2S,5S)-2-(tert-butyl)-5-phenyl-1,3-dioxolan-4-one 2b. Variable 4S/4R mixtures of (3R)-S-hydroxy-beta-lactams 4a,b are obtained, depending on the reaction conditions. The induced enantioselectivity (ee) is very high, and the simple selectivity (exo-endo) is low. Overall, this appears a rather direct approach to chiral beta-lactams with full control of stereochemistry at C3. The stereoselective radical reduction of the stereoisomer (3R,4R)-E-4a afforded the homochiral C3,C4-monosubstituted beta-lactam (3S,4S)-Z-10. (C) 1997 Elsevier Science Ltd.