Flavan derivatives. XXXIII. 2-Methoxyflavan-3,4-dione and 2-Methoxyflavan-3,4-diol derivatives

摘要: Sodium borohydride reduction of 3-hydroxy-7-benzyloxy-2,3,4'-trimethoxy-flavanone and of 3-hydroxy-2,3,7,4'-tetramethoxyflavanone is shown to yield mainly trans-trans-2-methoxyflavan-3,4-dials, a novel class of flavan derivatives. The 7-benzyloxy hemiacetal also gave a minor quantity of the cis-cis-2-methoxyflavan-3,4-dial and less of the corresponding 2,3-cis-flavan-3,4-trans-dial. Catalytic hydrogenation over palladium, or reduction with complex metal hydrides at room temperature or above, converted the hemiacetals into the flavonols from which they were originally prepared by oxidation with periodic acid in methanol.