SPECTROSCOPIC DETECTION OF AN ARYLCHLOROCARBENE ETHYL-ACETATE CARBONYL YLIDE AND SUBSEQUENT OXIRANE FORMATION

Laser flash photolysis of 3-chloro-3-(p-nitrophenyl)diazirine (1) generates the corresponding ground-state singlet carbene (lambda-max = 310 nm), which reacts with ethyl acetate to form a carbonyl ylide of the ester (lambda-max = 490 nm). The absolute rate constant for ylide formation in CH2Cl2 is k = (2.85 +/- 0.17) X 10(6) M-1 s-1. Subsequent cyclization of the ylide to the corresponding oxirane (lambda-max = 350 nm) occurs with a rate constant of 1.26 x 10(6) S-1 (21-degrees-C) in ethyl acetate with Arrhenius activation parameters for oxirane formation of E(act) = 6.68 +/- 0.19 kcal/mol and log A (s-1) = 11.08 +/- 0.15. The carbonyl ylide is also intercepted with the dipolarophile, diethyl fumarate, with a rate constant of (1.04 +/- 0.07) x 10(7) M-1 s-1. Additionally, solvent polarity effects on (p-nitrophenyl)chlorocarbene reactivity and spectroscopic evidence of oxirane formation (lambda-max = 350 nm) from the related acetone ylide of (p-nitrophenyl)chlorocarbene are presented.