Steady-state and laser photolysis studies of substituted 2H-azirines. spectroscopy, absolute rates, and arrhenius behavior for the reaction of nitrile ylides with electron deficient Olefins

The photobehavior of 2,2-diphenyl-3-methyl-2H-azirine (15) and 2-methyl-2,3-diphenyl-2ff-azirine (14) was investigated in solution at 298 K. Both azirines undergo ready ring opening on exposure to UV light to give nitrile ylides which can be trapped with methyl acrylate or methanol. In the absence of a trapping reagent, the ylide derived from azirine 15 undergoes 1,5-electrocyclization followed by a 1,3-sigmatropic hydrogen shift to give an isoindole derivative. The transient absorption spectra obtained after pulsed laser photolysis of azirines 14,15, and 2,3-diphenyl-2H-azirine (13) in isooctane at 298 K are in good agreement with those obtained at 77 K in a 3-methylpentane glass. Absolute quenching rate constants for reaction of the ylides derived from azirines 13-15 with acrylonitrile and fumanitrile are consistent with competitive quenching studies. The Arrhenius behavior for the reaction of the ylide derived from azirine 13 with methyl acrylate and diethyl fumarate gives evidence for reversible formation of an ylide-olefin complex.