Synthesis of enantiomerically pure α-amino-β-hydroxycyclobutanone derivatives and their transformations into polyfunctional three- and five-membered ring compounds

Ketenes readily cycloadded to (R)-tert-butyldihydrooxazole 2a-d to yield enantiomerically pure bicyclic cyclobutanones. The cycloadditions proceeded with unusual regiochemistry giving predominantly or exclusively protected alpha-amino-beta-hydroxycyclobutanone derivatives. The adducts could be converted into a variety of interesting enantiopure intermediates equipped with many functional groups: alpha-amino-beta-hydroxy cyclopropane carboxylic acid derivatives, alpha-amino-beta-hydroxy succinic acid derivatives, alpha-amino-beta-hydroxy lactones and lactams derivatives. (C) 2004 Elsevier Ltd. All rights reserved.