Diazafulvenones. Thermal Isomerizations and Eliminations in Alkoxycarbonyl and Anilinocarbonyl Derivatives of Imidazole

Article abstract of DOI:10.1021/jo00353a006

4-Carbonyl-4H-imidazole (10) and 2-carbonyl-2H-imidazole (11) are formed by flash vacuum pyrolysis of methyl 4- and 2-imidazolecarboxylates, respectively. 10 and 11 dimerize to diketopiperazines 14 and 16, respectively.The same products are also obtained from 4- and 2-(anilinocarbonyl)imidazoles, respectively.Methyl imidazole-1-carboxylate (4) on pyrolysis gives a ca. 1:1 mixture of the same ketenes 10 and 11, which dimerizes to a 1:2:1 ratio of diketopiperazines 14-16.In contrast, ethyl imidazole-1-carboxylate gave CO2, ethylene, and imidazole as the major products.The pyrolysis reactions were monitored by low-temperature infrared and high-temperature mass spectrometry.