Dehydro-intermediates in naphthalene chemistry.

The extension of benzyne chemistry to non ortho-dehydroarenes is discussed. The generation and reactions of the "meta"-dehydroarene, 1,8-dehydronaphthalene, are described and attempts made to correlate its properties with the possible electronic structures of dehydroaromatic intermediates. 1,8-Dehydronaphthalene was generated by oxidation of l-aminonaphtho[l,8-de]triazine and was shown to be a highly reactive species, readily undergoing radical abstraction reactions and 1,2-addition to a variety of unsaturated systems such as olefins, acetylenes, aromatic hydrocarbons and azo compounds. The stereospecificity of 1,2-addition to olefins was carefully investigated in an attempt to determine the singlet-triplet nature of 1,8-dehydronaphthalene. l-Aminonaphtho[l,8-de]triazine was prepared by direct amination of naphtho[l,8-de]triazine with hydroxylamine-o-sulphonic acid which also gave 8-azido-l-naphthylamine rather than the expected 2-aminonaphtho[l,8-de]triazine. However amination of the naphthotriazine with chloramine gave both 1- and 2 -aminonaphthotriazines, and the 2-amino isomer was shown to rearrange readily to 8-azido-l-naphthylamine under the alkaline conditions of the hydroxylamine-o-sulphonic acid amination, although it was stable to acid. In contrast 1-aminonaphthotriazine was stable to alkali but underwent an interesting acid catalyzed rearrangement to the same azide. Other possible, but unsuccessful, routes to 1,8-dehydronaphthalene were briefly investigated. Since 1,8-dehydronaphthalene was very different from benzyne generated similarly, 1,2-and 2,3-naphthyne were prepared by oxidation of the appropriate aminonaphthotriazole, to provide a more direct comparison. These two naphthynes closely resembled benzyne and were again significantly different from 1,8-dehydro-naphthalene. Their dimerisation in the absence of aryne "traps," and their crossed coupling with each other and with benzyne proved an attractive route to the dibenzo- and monobenzo-biphenylenes. The new heterocyclic system, benz[cd]indazole, was of interest as a possible product in the oxidations of 1- and2-aminonaphtho[l,8-de]triazines and as a possible precursor to1,8-dehydronaphthalene. Various attempts to obtain this and its dihydro derivative failed; however dimethyl dihydrobenz[cd]- indazole-1,2-dicarboxylate was formed by addition of 1,8-dehydronaphthalene to dimethyl azodicarboxylate. A novel oxazole synthesis is also described. Anomalies in the amination of benzotriazole with chloramine and hydroxylamine-o-sulphonic acid compared with similar amination of naphtho[l,8-de]triazine led to the isolation of 1-chlorobenzotriazole, which proved to be a reactive positive halogen compound and a convenient new oxidant.