The chemistry of fungi. Part LXIX. A new synthesis of the grisane system: X-ray crystallographic examination of (±)-methyl 5,7-di-bromo-2′α,5′α-epoxy-4-methoxy-3-oxogrisane-6′β-carboxylate

Abstract

Addition of furan to methyl 4-(2,6-dimethoxyphenyl)-4-oxobut-2-ynoate (4; R = CO₂Me) followed by hydrogenation of the adduct gave methyl 3-(2,6-dimethoxybenzoyl)-7-oxabicyclo[2.2.1]hept-2-ene-2-carboxylate (6; R = Me). This was demethylated to the corresponding 3-(2-hydroxy-6-methoxybenzoyl) derivative (6; R = H), which was cyclised by bases to give (a)(±)-methyl 2′α,5′α-epoxy-4-methoxy-3-oxogrisane-6′β-carboxylate (9; R = H), the structure of which was deduced chemically and spectroscopically, and unequivocally defined by X-ray crystallography, together with (b) the isomeric 6′α-carboxylate. Both grisanes were converted into (±)-methyl 2′α-hydroxy-3-oxogris-5′-ene-6′-carboxylate (11).