Die Synthese und der thermische Zerfall des 1,2-Diazabenzosemibullvalens und dessen Beziehung zur Thermolyse des Benzobenzvalens

Article abstract of DOI:10.1002/hlca.19860690317

The <4 + 2>-photoadduct of naphthalene and 4-phenyl-4H-1,2,4-triazol-3,5-dione (PTAD) was subjected to a triplet-sensitized di-?-methane rearrangement.Hydrolysis of the resulting urazol 15 gave a stable semicarbazide 16 which by nickel-peroxide oxidation gave 1,2-diazabenzosemibullvalene (10).At 40 deg C, the latter decays in CHCl3 solution to produce benzofulvene (2) as the principal product, accompanied by benzobenzvalene (1) and small amounts of naphthalene.This decay reaction is rationalized in terms of a 1,3-dipolar cycloreversion which is followed by denitrogenation to give indenyl carbene (9).The thermolysis of 1 in solution is believed to produceed via the same carbene.At present, these findings provide only a partial answer to the benzobenzvalene enigma (i.e., in solution at 150 deg C, 1 gives 2, but in the gas-phase at 300 deg C, 1 yields naphthalene).MeOH is shown to add readily to 10 in a homologous Michael addition.