Reactions of an imidazo[4,5-c]isoxazole-6-carboxylate with dimethyl acetylenedicarboxylate; formation of the first example of a [1,4]diazepino[2,3-c]isoxazole

The synthesis of the first example of a [1,4]diazepino[2,3-c]isoxazole derivative is reported. Reaction of an imidazo[4,5-c]isoxazole with acetylenic esters has been shown to lead to the formation of 2-pyrrol-2-yl imidazoles. Here we report an alternative reaction pathway in which the fused imidazole ring adds a molecule of acetylenic ester, and undergoes ring expansion to a fused [1,4]diazepine. A mechanism for the reaction is discussed.