ON THE REGIOSELECTIVITY IN NITRONE CYCLOADDITIONS TO GAMMA-OXO ALPHA,BETA-UNSATURATED ESTERS

The 1,3-dipolar cycloadditions of the cyclic nitrones 1 and 2 to sever al gamma-oxo alpha,beta-unsaturated eaters, 5-10, are reported. A stro ng predominance of the regioisomers with the oxygen atom of the dipole attached to the beta-ester position is observed. This high regioselec tivity is attributed to steric factors. The reduction of the carbonyl group of some of the major cycloadducts is a good yielding procedure f or the preparation of some hydroxylic derivatives that are not formed or obtained only as minor stereoisomers in the cycloadditions of the s ame nitrones to the corresponding gamma-hydroxy alpha,beta-unsaturated eaters. (C) 1998 Elsevier Science Ltd. All rights reserved.