A Convenient Synthesis of 4- and 5-Acetyltropolone

Article abstract of DOI:10.1246/bcsj.55.1594

4-Acetyltropolone is derived from hinokitiol (β-thujaplicin) in four steps, with an overall yield of 60percent, via readily available 8-azidohinokitiol. γ-Thujaplicin almost quantitatively forms its difluoroboron complex, which, upon bromination, provides an 85percent yield of the 8-bromo-γ-thujaplicin difluoroboron complex.This bromo compound readily gives γ-dolabrin (87percent with triethylamine) and 8-azido-γ-thujaplicin (88percent with sodium azide), from which 5-acetyltropolone is derived in an 80percent yield by ozonolysis or in 40percent yield with sulfuric acid.The considerable differences in the reactivities observed between these 4- and 5-substituted tropolones are discussed.The pK_a values of 4- and 5-acetyltropolone and 4- and 5-(3,4,5-trimethoxycinnamoyl)tropolones are also reported.