Flash vacuum pyrolysis of 2-acetyl-3-azido[1]benzothiophene

Abstract

Flash vacuum pyrolysis (FVP) of 2-acetyl-3-azido [1]benzothiophene at 300 °C provides 3-methyl [1]benzothieno[3,2-c]isoxazole (72%). At higher temperatures, the heteroindoxyl 1,2-dihydro[1]benzothieno[3,2-b]pyrrol-3-one was obtained in low yield (ca. 10%). The heteroindoxyl exists as a mixture of keto and enol forms in DMSO solution. Because of the easy oxidative dimerisation of these products to indigotin (and its heteroanalogues), such reactions are excellent examples of the synthetic advantages of FVP with the monomeric products conveniently generated under vacuum in a solvent -free, air-free environment.