Total syntheses of three natural products, vignafuran, 2-(4-hydroxy-2-methoxyphenyl)-6-methoxybenzofuran-3-carboxylic acid methyl ester, and coumestrol from a common starting material

Vignafuran 2, 2-(4-hydroxy-2-methoxyphenyl)-6-methoxybenzofuran-3-carboxylic acid methyl ester 3, and coumestrol 4 were efficiently synthesized from the same starting material, 4-bromoresorcinol 14a, through the common intermediate, diarylacetylene 7. The key steps of these syntheses were the tetrabutylammonium fluoride (TBAF)-catalyzed benzo[b]furan ring formation for 2 and the carbonylative ring closure methodology catalyzed by a Pd complex for 3 and 4.