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.

No abstract

“The acetotropy” of 2-acetoxytropones was shown to be a concerted [1,9] sigmatropic process on the basis of a kinetic analysis. A little substituent effect for the activation free energy of the acetyl migration was recognized. Preferred tautomers of polyacetoxytropones were those having the carbonyl group at inner positions. As an extreme case, a “Merry-Go-Round”-type rearrangement was operative in hexaacetoxytropone.

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The first and the second half-wave potentials of p-tropoquinones measured by CV are linear to the Hammett’s Σσp and Σσm, respectively. Their smaller electrostatic repulsion than p-benzoquinones can be attributable to the characteristic three carbonyl system.