Intermolecular Reactions of β-Lactam-4-ylidenes with Alkenes, Alcohols, and Acetic Acid. Spiro-Fused β-Lactam Cyclopropanes, 4-Alkoxy β-Lactams, and a 4-Acetoxy β-Lactam

Article abstract of DOI:10.1021/jo00094a017

Thermolysis of spiro-fused β-lactam oxadiazolines in the presence of alkenes gave spiro-fused β-lactam cyclopropanes.The latter arise through a sequence of reactions beginning with 1,3-dipolar cycloreversion of an oxadiazoline to form N2 and a short-lived carbonyl ylide.The latter fragments to acetone and a β-lactam-4-ylidene, which adds to the alkene.Stereospecific additions to dimethyl fumarate and to dimethyl maleate are consistent with a concerted mechanism of cyclopropanation.The ylidenes also form cyclopropanes with alkenes that are not Michael acceptors, including styrene and 4-bromo-1-butene.Thermolysis of β-lactam oxadiazolines in the presence of hydroxylic compounds led to capture of β-lactam-4-ylidenes by OH insertion, essentially in quantitative yields, as expected for reaction of singlet β-lactam-4-ylidenes.