Structure and photochemical behaviour of 3-azido-acrylophenones: a matrix isolation infrared spectroscopy study

(Z)-3-Azido-3-methoxycarbonyl-2-chloro-acrylophenone (MACBP) has been synthesized, isolated in low temperature argon and xenon matrices and studied by FTIR spectroscopy, complemented by DFT(B3LYP)/6-311++G(d,p) calculations. The molecule was characterized both structurally and spectroscopically, and its photochemistry used to probe the mechanism of photo-induced conversion of 3-azido-acrylophenones into oxazoles. In situ UV irradiation (λ = 235 nm) of matrix-isolated MACBP yielded as primary photoproduct a 2H-azirine, which undergoes subsequent photoisomerization to methyl 4-chloro-5-phenyl-1,3-oxazole-2-carboxylate. In a competitive process, a ketenimine is also formed upon photolysis of MACBP. The reported results indicate that this ketenimine must be formed from the starting 3-azido-acrylophenone via a Curtius type concerted rearrangement.