Generation and Study of Benzylchlorocarbene from a Phenanthrene Precursor

• Published in: Journal of the American Chemical Society Vol. 120; no. 32; pp. 8055 - 8059
• Main Authors: Nigam, Manisha, Platz, Matthew S, Showalter, Brett M, Toscano, John P, Johnson, Richard, Abbot, Sarah C, Kirchhoff, Mary M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 19.08.1998
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja980251w

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.