Photochemistry of Matrix Isolated Methyl 3-Methyl 2H-Azirine-2-Carboxylate Studied by FT-IR and DFT Methods

A. KACZOR, A. GÓMEZ-ZAVAGLIA, A. L. CARDOSO T. M. V. D. PINHO E MELO AND R. FAUSTO.

Estambul, Turquía

Congreso; European Congress on Molecular Spectroscopy. EUCMOS 2006; 2006

Eucmos

The novel aliphatic 2H-azirine – methyl 3-methyl-2H-azirine-2-carboxylate (MMAC) has been synthesized and its monomeric structure has been determined in the argon matrix at 10 K. Two conformers – Cc and Ct (the capital and lower-case letters denote the conformation in respect to C-O and C-Ca bonds, respectively) were found in the matrix, with the Cc form being slightly stabilized compared with the Ct one (see the figure). In situ broadband UV (l> 235 nm) excitation of the isolated compound resulted in cleavage of the C-C or C-N bond, leading to formation of nitrile ylide (P1) or ketene imine (P2) type of products, respectively (c. f. figure) [Agnieszka: for consistency with the paper on MCMAC, I interchanged P1 and P2]. The C-N cleavage, unusual for aliphatic 2H-azirines, was previously observed for methyl 2-chloro-3-methyl-2H-azirine-2-carboxylate and attributed to the simultaneous presence of two electron-withdrawing substituents (methylcarboxy group and chlorine atom), accelerating the intersystem crossing toward the triplet state and – in this way - C-N breakage [1]. Nevertheless, the study of photochemistry of MMAC allowed separating the effect of substituents, showing that the methylcarboxy group plays a crucial role in photochemical behavior of above-mentioned azirines.