Conformational behaviour, photochemistry and flash vacuum pyrolysis of a 2-(1H-tetrazol-1-yl)thiophene

Abstract

The conformational properties and the photochemical behaviour of a 2-(1H-tetrazol-1-yl)thiophene were studied using low-temperature matrix isolation (argon; 16 K) coupled with infrared spectroscopy. The experimental results were supported by theoretical calculations carried out at the B3LYP/6-311++G(d,p) level. The calculations predicted two conformers for the studied compound in the gas phase that differ in energy by 3.2 kJ mol⁻¹. Accordingly, two conformers were observed in the low-temperature matrix. UV-laser irradiation at 245 nm of the studied compound isolated in the argon matrix led to photocleavage of the tetrazole ring, with elimination of N₂ and formation of the corresponding thiophen-2-ylcarbodiimide, most likely via the corresponding imidoylnitrene intermediate. The flash vacuum pyrolysis of 2-(1H-tetrazol-1-yl)thiophene gave methyl 1H-thieno[2,3-d]imidazole-1-carboxylate via intramolecular formal insertion into a C–C bond of the corresponding imidoylnitrene intermediate and the unexpected 2-methoxythieno[2,3-d]pyrimidin-4(3H)-one. The synthesis of this heterocycle was rationalized considering the initial N₂ elimination to generate an imidoylnitrene followed by rearrangement to the corresponding thiophen-2-ylcarbodiimide, [1,5] sigmatropic shift of the methoxyl group and electrocyclic ring closure.