Naturally occurring dibenzofurans. Part 4. Synthesis of dibenzofurandiols by annelation of benzofurans

Abstract

Methyl3-acetylbenzofuran-2-ylacetate(8)undergoes C-methylationaffordingmethyl2-(3-acetylbenzofuran-2-yl)propionate (13). These compounds and similar oxo esters undergo ready cyclization to dibenzofurandiols on treatment with sodium methoxide in boiling methanol. A convenient synthesis of dimethyl furan-2,5-diyldiacetate (30) is described, as are attempts to synthesize 1,3,7,9-tetramethoxy-2,8-dimethyldibenzofuran (3).