A synthesis of bikaverin (7,12-dihydro-6,11-dihydroxy-3,8-dimethoxy-1-methyl-10H-benzo[b]xanthene-7,10,12-trione) and some related benzoxanthones and quinones

Abstract

Bikaverin, a biologically interesting fungal pigment with the highly oxidised benzoxanthone structure (1), has been synthesized in two steps from 2-hydroxy-4-methoxy-6-methylacetophenone (6f) and dimethyl 3,5-dimethoxyhomophthalate (7f). The synthesis involves a base-catalysed reaction between these substrates to give the substituted 11-hydroxybenzoxanthone (8f) in about 25% yield, followed by oxidation of the latter with trifluoroperacetic acid under controlled conditions directly to bikaverin in about 35% yield. The operational simplicity, together with the easy accessibility of the starting materials, make this synthesis compare favourably with two, previously reported syntheses of bikaverin. The preparation of five additional 11-hydroxybenzoxanthones, and the oxidative conversions of four of these, are also described.