Spectroscopic detection of an arylchlorocarbene-ethyl acetate carbonyl ylide and subsequent oxirane formation

Article abstract of DOI:10.1021/ja00017a033

Laser flash photolysis of 3-chloro-3-(p-nitrophenyl)diazirine (1) generates the corresponding ground-state singlet carbene (λ_max = 310 nm), which reacts with ethyl acetate to form a carbonyl ylide of the ester (λ_max = 490 nm). The absolute rate constant for ylide formation in CH₂Cl₂ is k = (2.85 ± 0.17) × 10⁶ M^-1 s^-1. Subsequent cyclization of the ylide to the corresponding oxirane (λ_max = 350 nm) occurs with a rate constant of 1.26 × 10⁶ s^-1 (21 °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 dipdarophile, diethyl fumarate, with a rate constant of (1.04 ± 0.07) × 10⁷ M^-1 s^-1. Additionally, solvent polarity effects on (p-nitrophenyl)chlorocarbene reactivity and spectroscopic evidence of oxirane formation (λ_max = 350 nm) from the related acetone ylide of (p-nitrophenyl)chlorocarbene are presented.