FORMATION AND STRUCTURE OF 2-DIAZO-2,4-AZULENEQUINONE DERIVATIVES

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 derivatives (5 and 6). The diazo carbons of both 5 and 6 show C-13 NMR signals at delta 66.3, and their carbonyl carbons resonate at 6 181.1, in good agreement with a 2-diazo-2,4-azulenequinone structure. The structures of diazo compounds 24 and 25, which we have previously reported,(1) are reexamined on the basis of the analysis of their C-13 NMR spectra. The contribution of a quinoid structure and a diazoazulenolate structure to 5, 6, 24, and 25 is discussed by comparison of their C-13 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.