The chemistry of fungi. Part 77. The synthesis of benzophenones from phthalides : X-ray crystallographic definition of a novel isobenzofuran system

Abstract

Reduction of 3,6-dimethoxy-4-methylphthalic anhydride gave a mixture of 3,6-dimethoxy-4-methyl-(1; R¹= H, R²= Me) and 3,6-dimethoxy-5-methyl-(1; R¹= Me, R²= H) phthalide.

The condensation of 2,6-dimthoxylithiobenzene with phthalides gives the corresponding 2′-hydroxymethyl-2,6-dimethoxybenzophenones. Treatment of 6-acetoxymethyl-2,5-dibenzyloxy-2′,6′-dimethoxy-4-methylbenzophenone (11; R = H) with boron trichloride gives 1-(2-hydroxy-6-methoxyphenyl)-5-methyl-4,7-dioxo-4,7-dihydroisobenzofuran (13; R = H), the structure of which was defined by X-ray analysis. The crystals are monoclinic, space group P2₁ with two molecules in a unit cell of dimensions a= 10.818(1), b= 7.752(1), c= 7.808(3)Å, and β= 90.28(1)°. The structure was solved by the direct method using 1 257 reflections and refined by full-matrix least-squares calculations to R= 0.053.