Formation and Structure of 2-Diazo-2,4-azulenequinone Derivatives

Article abstract of DOI:10.1021/jo00123a031

The diazotization of methyl (and ethyl) 2-amino-3-cyano-4-methoxy(and ethoxy)azulene-1-carboxylate (1-4) was examined to determine whether the products are 2-diazo-2,4-azulenequinone derivatives (B) or azulene-2-diazonium-1-carboxylate derivatives (C).Since diazotization of 1 and 2 gave the same diazo compound 5 and diazotization of both 3 and 4 gave diazo compound 6, the diazo compounds are deduced to not be azulene-2-diazonium-1-carboxylate derivatives (7 and 8), but rather to be 2-diazo-2,4-azulenequinone (5 and 6).The diazo carbons of both 5 and 6 show 13C NMR signals at δ 66.3, and their carbonyl carbons resonate at δ 181.1, in good agreement with a 2-diazo-2,4-azulenequinone structure.The structures of diazo compounds 24 and 25, which we have previously reported, are reexamined on the basis of the analysis of their 13C NMR spectra.The contribution of a quinoid structure and a diazoazulenoeate structure to 5, 6, 24, and 25 is discussed by comparison of their 13C NMR spectral data with those of 4-diazo-2,5-cyclohexadien-1-one derivatives.It is concluded that the contribution of the quinoid structure is larger than that of the diazoazulenolate structure.