Preparation of isobenzofuran-1(3H)-ones by decarbonylation of 1H-2-benzopyran-1,3(4H)-diones

Abstract

3,3-Dimethyl-1H-2-benzopyran-1,3(4H)-dione (3,3-dimethylhomophthalic anhydride) is decarbonylated in the presence of aluminium chloride to give 3,3-dimethylisobenzofuran-l(3H)-one (3,3- dimethylphthalide) in good yield. The 5,8-difluoro anhydride reacts similarly to give the 4,7- difluoro lactone. The precursors of the anhydrides, the 3,3-dimethyl-2,3-dihydro-1H-inden-1-ones, were prepared from 3-methylbut-2-enoic acid and the appropriate aromatic compound in the presence of aluminium chloride. The difluorodihydroindenone prepared in this way is accompanied by 5,8-difluoro-4-methyl-3,4-dihydronaphthalen-1(2H)-one and a mechanism is proposed to account for its formation.