The palladium-catalyzed reduction of various N-arenesulfonylaziridines bearing alpha,beta-unsaturated ester groups with formic acid and the stereochemistry of the reaction products have been investigated in detail. In all cases examined, (Z)-alpha,beta-enoates, (E)-alpha,beta-enoates, and (E)-beta,gamma-enoates bearing amino functionality at the delta-position were obtained. The formation of these three reduction products was taken as an indication that palladium-catalyzed isomerization occurs prior to the reduction step. (C) 1997 Elsevier Science Ltd.