Arynes definition

Didehydropyridine (97) is less well investigated, and the existence of this intermediate is not yet established definitively. Aryne 97 has been postulated as an intermediate in the gas-phase pyrolysis of 2,3-pyridinedicarboxylic anhydride (107) at 600 °C, which hnally yields (3-ethinyl acrylonitrile (108). Indirect evidence stems from trapping experiments with benzene and thiophene. Photolysis of matrix isolated 107 does not produce 97 (Scheme 16.25). Nam and Leroi ... 

Tetrachlorophthalic anhydride gave a relatively low yield of products derived from tetrachlorobenzyne. The pyrolysis tube was badly carbonized evidently extensive decomposition of the anhydride, the aryne, or the chlorinated products had occurred. Tetrabromophthalic anhydride gave a still lower yield of products. These are not listed in the table because none of them retained all four bromine atoms and could be definitely ascribed to reactions of tetrabromobenzyne, although tri-bromo- and dibromonaphthalene were present in appreciable amounts. Tetraphenylphthalic anhydride also gave low yields of products of the reaction of tetraphenylbenzyne with pyridine. This was not because of the stability of the anhydride and its reluctance to form the aryne, but rather because the aryne preferred to stabilize itself intramolecularly. The behavior of tetraphenylphthalic anhydride is discussed in another Section. 

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