The preparation and antimicrobial activity of a series of beta-lactams (3a-f) are described. These compounds were prepared from the 2+2 cycloaddition of beta,beta-disubstituted enamines with aryl isocyanates; compounds 3a-f underwent facile beta-lactam ring fission between aminal carbon atom C4 and the lactam nitrogen N1. The resisting formylacetanilide derivatives were devoid of antibiotic activity.

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Two synthetic procedures have been developed for the preparation of azeto[1,2‐a]quinoxaline‐ 1,3‐diones, a novel class of fused heterocyclic β‐lactams possessing a bridgehead nitrogen atom. Both processes are general and afford the title compounds in good yield. The infrared, proton magnetic resonance, and mass spectroscopic properties of the title compounds are discussed.