The curved plots of (carbene adduct)/(carbene-rearrangement product) versus carbene trapping agent, tetramethylene [TME], reported with benzylchlorodiazirine 1 have been reproduced. However, with the use of a non-nitrogenous precursor, plots of this type are approximately linear over the range of [TME] employed. Thus, any complex formed between benzylchlorocarbene and TME must collapse to form cyclopropane faster then it can fragment with rearrangement to β-chlorostyrene and TME. Diazirine 1 does photoisomerize to diazo compound 7, but this process is inefficient (φ = 0.075) and is not likely to be responsible for the curvature in plots of adduct/styrene versus [TME] observed with the diazirine precursor. Thus, the second, noncarbene, pathway to β-chlorostyrene is neither a carbene−olefin complex nor a diazo intermediate. It is proposed that the second pathway involves a rearrangement in the excited state of the diazirine, although other explanations cannot be discarded.

Laser flash photolysis (308 nm) of carbomethoxy-2-naphththyldiazomethane in deoxygenated Freon-113 (CF2ClCFCl2) solution containing tetrahydrofuran (THF) produces a transient spectrum with a sharp absorption maximum at 330 nm and a shoulder at 375 nm. The observed rate constant of formation of transient absorption is the same at 330 and 400 nm. The transient spectrum is the same 100 ns, 1 μs, and 10 μs after the laser pulse at ambient temperature and is attributable to a single carrier. The transient shows little decay over 10 μs in the presence and absence of oxygen. Similar results were obtained at −60° C. This pattern of observations is not consistent with assigning the transient to triplet carbomethoxy-2-naphthylcarbene or its related radical. The rate constant of formation of the transient, k THF, is first order in the concentration of THF; thus, the transient is attributed to a carbene−ether ylide. To our knowledge, this is the first direct observation of a carbene-ether ylide. An Arrhenius plot of k THF is nonlinear due to a change in mechanism of the reaction of the carbene with THF or to reversion of the ylide to carbene and THF at elevated temperatures.

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