Syntheses of 2,4-dihydroxy- and 1,3-dihydroxy-8-methylphenanthrene-9,10-quinones and their bearing on the structure of denticulatol

Abstract

Wittig reaction of (2-methylbenzyl)triphenylphosphonium bromide, 3,5-dimethoxybenzaldehyde, and lithium methoxide gave 3,5-dimethoxy-2′-methylstilbene (V), which on photo-cyclodehydrogenation afforded 2,4-dimethoxy-8-methylphenanthrene (VI). Demethylation of this phenanthrene followed by acetylation furnished 2,4-diacetoxy-8-methylphenanthrene (VII), which on chromium trioxide oxidation and hydrolysis gave 2,4-dihydroxy-8-methylphenanthrene-9,10-quinone (III). A similar route gave 1,3-dihydroxy-8-methylphenanthrene-9,10-quinone. Neither quinone had properties corresponding to those reported for denticulatol.