Preparation of Polyacetoxytropones and Polyhydroxytropolones by Acetolysis and Hydrolysis of Halotroponoids by Acetyl Trifluoroacetate with Exhaustive Displacement of Halogens on the Tropone Ring. Predominant Formation of Reductive Acetolysates from Fully-Substituted Tropones

Article abstract of DOI:10.1246/bcsj.60.4325

Di-, tri-, and tetrahydroxytropolones were prepared in good yields by the acetolysis of corresponding halotropones or polyhalotropolones with acetyl trifluoroacetate followed by acetic acid hydrolysis.However, using the same treatment to obtain hexaacetoxytropone with fully substituted acetoxyhalotropones predominantly yielded fewer substituted acetoxytropones than expected; the mechanism of formation was shown to involve an acetic acid-mediated reduction of intermediary formed acetoxy-p-tropoquinone equivalents.A couple of 2,7-unsubstituted 3,4-diacetoxytropones were deduced to have cyclized 1,3-dioxole structures, 2-acetoxy-2-methyl-5H-cyclohepta-1,3-dioxol-5-ones.An acetolysis of the brominated 5-isopropyltropolones furnished an acetylated by-product, 2,3,7-triacetoxy-5-(1,1-dimethyl-2-oxopropyl)tropone, which might be formed by the acylation of an intermediate, 3,4,5,6-tetraacetoxy-8,8-dimethylheptafulvene.