group at the 5-position, 4-substituted2-(2-arylhydrazino)tropones were obtained as the major products by the abnormal substitution reaction. These 2-(2-arylhydrazino)tropones are expected to effectively serve as precursors for a convenientsynthesis of 5-aryl-substituted tropolones via benzidine-type rearrangement. 1H NMR (200 or 500-MHz) parameters for these 4-substituted2-(2-arylhydrazino)tropones
sodium azide), from which 5-acetyltropolone is derived in an 80% yield by ozonolysis or in a 40% yield with sulfuric acid. The considerable differences in the reactivities observed between these 4- and 5-substituted tropolones are discussed. The pKa values of 4- and 5-acetyltropolone and 4- and 5-(3,4,5-trimethoxycinnamoyl)tropolones are also reported.