An efficient synthesis of 3,5-dimethoxyhomophthalic acid, a key intermediate for synthesis of natural isocoumarins

3,5‐Dimethoxyhomophthalic acid was prepared efficiently in three steps, from 3,5‐dimethoxybenzyl bromide via rhodium‐catalyzed direct carbonylation to 3,5‐dimethoxyphenylacetic acid followed by successive o ‐formylation and oxidation. Isocoumarins related to agrimonolide and achlisocoumarin 1 were prepared in single step by condensation of the homophthalic acid with appropriate acid...