Naturally occurring dibenzofurans. Part 2. The synthesis of schizopeltic acid

Abstract

The structure of schizopeltic acid as 1,7-dimethoxy-6-methoxycarbonyl 3,9-dimethyldibenzofuran-4-carboxylic acid (1) has been confirmed by rational synthesis. 6-Methoxy-4-methylbenzofuran-2-carbaldehyde (10), available from 3,5-dimethoxytoluene (4) in six steps, was converted into methyl 1-acetoxy-7-methoxy-9-methyldibenzofuran-3-carboxylate (12) by Wittig reaction with 2-carboxy-1-methoxycarbonylethyltriphenylphosphorane and subsequent ring-closure of the resultant (E)-3-methoxycarbonyl-4-(6-methoxy-4-methylbenzofuran-2-yl)but-3-enoic acid (11) with acetic anhydride. Reduction of compound (12) gave 7-methoxy-3,9-dimethyldibenzofuran-1-ol (14) which was converted into schizopeltic acid (1) by sequential formylations and oxidations.