Regio- and stereoselective synthesis of constrained enantiomeric β-amino acid derivatives

Chlorosulfonyl isocyanate addition to (-)- and (+)-apopinene furnished monoterpene-fused beta-lactams in highly regio- and stereospecific reactions. beta-Lactams 5 and 13 exhibited reactivities similar to those of the cycloalkane-fused analogs and were easily converted to the p-amino acid and its protected derivatives. The base-catalyzed isomerization of the cis-amino ester afforded the corresponding trans-amino acid enantiomers in excellent yields. The complete isomerization is explained by the stability difference, which was estimated by ab initio calculations between the cis- and trans-diastereomers. (C) 2008 Elsevier Ltd. All rights reserved.