Methyl 3-methyl-2H-azirine-2-carboxylate photochemistry studied by matrix-isolation FTIR and DFT calculations

The aliphatic 2H-azirine, methyl 3-methyl-2H-azirine-2-carboxylate (MMAC), has been synthesized and its monomeric form investigated by IR spectroscopy in an argon matrix, at 10 K, as well as theoretically (DFT/B3LYP/6-311++G(d,p)). Two low-energy conformers of MMAC (Ct and Cc) were found in the matrix, both exhibiting the cis conformation around the C-O bond but differing in the arrangement around the C-C(alpha) bond. The two conformers were photoreactive upon in situ broadband UV excitation (lambda > 235 nm), yielding nitrile ylide (P1) and ketene imine (P2) type products, which resulted from cleavage of the C-C or C-N bond, respectively. The kinetics of the reactions leading to the formation of P1 and P2 are of first order, with the processes being favored when the reactant is in the Cc conformation. Very interestingly, the C-N bond photocleavage, which is unusual for aliphatic 2H-azirines, was found to be preferred over the generally favored in 2H-azirines C-C bond breakage. This behavior is attributed to the presence in the molecule of the electron-withdrawing methoxycarbonyl substituent, which accelerates the intersystem crossing toward the T(1) triplet state and, in this way, favors the C-N bond cleavage. In addition to the primary photoprocesses leading to formation of P1 and P2, secondary photoprocesses leading to the decarboxylation and decarbonylation of P2 have been also observed.Fil: Kaczor, Agnieszka. Universidad de Coimbra; Portugal. Jagiellonian University; PoloniaFil: Gomez Zavaglia, Andrea. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina. Universidad de Coimbra; Portugal. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; ArgentinaFil: Cardoso, Ana Laura. Universidad de Coimbra; PortugalFil: Pinho E Melo, Teresa M. V. D.. Universidad de Coimbra; PortugalFil: Fausto, Rui. Universidad de Coimbra; Portuga