Reaction of cyclohexanone benzylimines with ethylidenemalonate diesters. Diphenyl 2-ethylidenemalonate: A highly electrophilic synthetic equivalent of crotonic esters

The diastereoselective Michael alkylation of alpha -substituted and alpha,a lpha'-disubstituted cyclohexanone benzylimines with ethylidenemalonate dies ters was carried out for mechanistic and synthetic purposes. In the first c ase, an inverse regioselectivity occurred in comparison with what is genera lly observed since the Michael adducts resulted from alkylation of the non substituted enamine tautomer. With a,a'-disubstituted imines, in all cases, the stereochemistry of the major diastereomer was the one anticipated from a mechanism including a chairlike complex approach with a preferred exo po sition for the B-methyl group of the ethylidenemalonic acid diesters. Furth ermore, diphenyl 2-ethylidenemalonate 4 was found to be a highly electrophi lic synthetic equivalent of crotonic esters.