Characterization of a Stable Carboxylic Acid Intermediate from 1,3-Dipolar Cycloaddition of a Munchnone with 1,2-Dicyanocyclobutene

Article abstract of DOI:10.1021/jo00277a010

Reaction of 1 and 2 in acetic anhydride at 110 deg C produced intermediate 6, which captured the exo stereochemistry of the unseen primary cycloadduct, 5.Thermolysis of 6 at a much higher temperature readily gave the expected dihydroazepine 4.The stereochemistry of 6 was unambiguously established by the single-crystal X-ray analysis of methyl ester 8, formed by treating 6 with diazomethane under mild conditions.The isolation of 6 suggests that elimination of carbon dioxide from such primary cycloadducts need not be a concerted process.