Synthesis of 8-hydroxy-6-methoxy-3-pentyl-1H-isochromen-1-one from Tessmannia densiflora

The synthesis of 8-hydroxy-6-methoxy-3-pentyl-1H-isochromen-1-one (1) isolated from the stem and root bark extracts of Tessmannia densiflora has been described. The reaction of 3,5-dimethoxyhomophthalic anhydride (2) with hexanoyl chloride in the presence of 1,1,3,3-tetramethylguanidine and triethylamine afforded 6,8-dimethoxy-3-pentylisocoumarin (3). Regioselective demethylation of the latter using anhydrous aluminum chloride furnished the title isocoumarin (1).