摘要:
Titanium enolate-mediated aldol reaction of N-phthaloyl-beta-alanyl-1, 3-benzoxazinone 5 with acetaldehyde gave the (+/-)-syn-aldol (+/-)-6 in a high yield with high diastereoselectivity. Lipase-catalyzed hydrolysis of the corresponding laurate (+/-)-7b furnished enantiomerically pure (2S, 3R)-N-(2-phthaloylaminomethyl-3-hydroxybutyryl)-1, 3-benzoxazinone 6 in 49% yield. Silylation of the hydroxy group of (29, 3R)-6 follwed by deprotection of the amino and carboxy groups gave the beta-amino acid derivative 9 which was transformed into the acetoxyazetidinone 3, a key intermediate of penems and carbapenems. Copyright (C) 1996 Elsevier Science Ltd