N-Acylation of 4-alkylidene-beta-lactams: unexpected results

This paper describes the different reactivity of E- and Z-4-alkylidene-beta-lactams in acylation reactions under basic conditions. The E isomer is readily acylated, whereas the Z reacted sluggishly rearranging to the corresponding oxazin-6-one. The N-acylation of Z isomers was successfully obtained with oxalyl- or malonyl chlorides in benzene at reflux.