Ring contraction of 1,2,4-triazepino[2,3-a]benzimidazol-4-ones. New fused .beta.-lactams

Isolation of uncommon fused tetracyclic β-lactams 2 strongly supports a previously unconfirmed ionic mechanism for the ring contraction of nitrogen-bridged azolo-1,2,4-triazepin-3-ones in acetic anhydride. Procedures for the synthesis in good yields of substituted-pyrazolo [1,5-a] benzimidazoles from the corresponding [1,2,4] triazepino [2,3-a] benzimidazoles are reported