Structure and reactivity of arynes.

Known methods of generating arynes, and their chemical reactions, have been classified, and some new syntheses and reactions are described. A series of substituted 1-aminobenzotriazoles were synthesised from the corresponding o-nitroanilines by considerable modification of the literature method. These compounds were also synthesised by the amination of the corresponding benzotriazoles, using hydroxylamine-o-sulphonic acid. This reaction afforded the isomeric 2-aminobenzotriazole in the unsubstituted case only. Oxidation of the substituted 1-aminobenzotriazoles with lead tetra-acetate was accompanied by elimination of nitrogen from the nitrene initially formed, to yield the free aryne. The degree of dimerisation of the arynes, to give the corresponding biphenylenes, was found to vary with the substitution of aryne. 3-Nitrobenzyne afforded no dimer, forming instead 3-nitrophenyl acetate. Benzyne and 4-methoxybenzyne were shown to react as a symmetric singlet by the stereospecificity of the reaction with trans, trans-hexa-2,4-diene. Evidence for the existence of 3-nitrobenzyne in this electronic state was also found; semi-empirical calculations predicted benzyne, 4-nitrobenzyne and 3-nitrobenzyne to exist in the singlet ground state. The reactivities of several arynes were compared by the relative degree of 2 + 2 cycloaddition to vinyl acetate. 3-Nitrobenzyne was found to be highly reactive; semi-empirical calculations showed that this species had an unusually high dipole moment, and the reactivity was explained in terms of the polarity between the non-bonded o-orbitals. Evidence for the intermediacy of 2,2'-dehydrobiphenyl in the dimerisation of benzyne was found. Certain arynes cleaved dialkyl ethers to give the phenyl alkyl ether. The "ene" reaction was extended to acetylenes, phenyl allenes being the products. Evidence for the existence of a transient ruthenium-benzyne complex was found, as was evidence of interaction between benzyne and silver or mercury.