Theoretical Study on the Transition-Metal-Catalyzed Cycloadditions of 2H-Azirines with Alkynes: Implication of Carbenoid Intermediates

Abstract

Abstract The ruthenium-catalyzed cycloadditions of 2,3-diphenyl-2H-azirine with dipropargyl ether or methyl 2-butynoate were investigated by performing density functional theory (DFT) calculations, and plausible mechanisms were proposed for each reaction. As the initial step, the oxidative coupling of dipropargyl ether and the oxidative addition of the 2H-azirine were first examined in order to explain the experimentally observed [3+2+2] vs. [3+2] selectivity. Subsequently, each step including the [3+2+2] and [3+2] cycloadditions was examined to determine the feasibility of these catalytic reactions. Moreover, the related gold-catalyzed [3+2] cycloaddition of an ynamide with 3-phenyl-2H-azirine was also evaluated using DFT calculations for comparison with the ruthenium-catalyzed [3+2] cycloaddition.