The regiospecific synthesis of an anthraquinone based upon the elaboration of the adduct of 1-acetoxyisobenzofuran with p-benzoquinone monoacetal

Abstract

1-Acetoxyisobenzofuran (4) reacts regiospecifically with 4,4-dimethoxycyclohexa-2,5-dienone (p-benzoquinone monoacetal) (6) to yield a single [4π+2π] cycloadduct with endo stereochemistry. Treatment of this adduct (7) with sodium methoxide formed 1,10-dihydroxy-4,4-dimethoxy-4a,10- dihydroanthracen-9(4H)-one (12), which was oxidized by the Corey-Fleet reagent to afford 1-hydroxy-4-methoxyanthracene-9,10-dione. This model reaction illustrates the potential of this approach to the regiospecific synthesis of anthraquinones. Attempts to introduce methoxy substituents into the anthraquinone by using 4- and 7-methoxy-1-acetoxyisobenzofuran, isobenzofurans described for the first time, were less successful. This limitation is discussed.