INTERMOLECULAR REACTIONS OF BETA-LACTAM-4-YLIDENES WITH ALKENES, ALCOHOLS, AND ACETIC-ACID - SPIRO-FUSED BETA-LACTAM CYCLOPROPANES, 4-ALKOXY BETA-LACTAMS, AND A 4-ACETOXY BETA-LACTAM

Thermolysis of spiro-fused beta-lactam oxadiazolines in the presence o f alkenes gave spiro-fused beta-lactam cyclopropanes. The latter arise through a sequence of reactions beginning with 1,3-dipolar cyclorever sion of an oxadiazoline to form N-2 and a short-lived carbonyl ylide. The latter fragments to acetone and a beta-lactam-4-ylidene, which add s to the alkene. Stereospecific additions to dimethyl fumarate and to dimethyl maleate are consistent with a concerted mechanism of cyclopro panation. The ylidenes also form cyclopropanes with alkenes that are n ot Michael accepters, including styrene and 4-bromo-1-butene. Thermoly sis of beta-lactam oxadiazolines in the presence of hydroxylic compoun ds led to capture of beta-lactam-4-ylidenes by OH insertion, essential ly in quantitative yields, as expected for reaction of singlet beta-la ctam-4-ylidenes.