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43.3.2 Product Subclass 2: 1,3-Didehydroarenes and 1,3-Didehydrohetarenes

DOI: 10.1055/sos-SD-043-00126

Gilchrist, T. L.Science of Synthesis, (200843206.

Whereas trapping experiments provide the overwhelming body of evidence for the generation of benzyne and other arynes in solution, such evidence is not generally available for 1,3-didehydrobenzene and other 1,3-didehydroarenes because there are no typical patterns of reactivity. Abstraction of hydrogen atoms and other radical reactions occur with low efficiency, and 1,3-didehydrobenzene is relatively unreactive toward reagents of other types.[‌261‌] Instead, the evidence for the existence of these species is based mainly on characterization through matrix-isolation experiments and mass-spectrometric methods. Matrix-isolated 1,3-didehydrobenzenes can be characterized by IR spectroscopy, in particular by the strong ring deformation absorption at 545±2cm1, which is almost unaffected by fluorine or methyl substituents at the 5-position.[‌262‌] Flash-pyrolysis methods can also be used to generate 1,3-didehydrobenzene (11). A characteristic final product from these reactions is the Z-enediyne 193 formed by ring-opening and hydrogen-shift reactions (Scheme 65).[‌263‌]

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