The chemistry of homophthalic acid: a new synthetic strategy for construction of substituted isocoumarin and indole skeletons

Homophthalic acid was reacted with thionylchloride/DMF and chloroethylformate/NEt₃ in the presence and absence of NaN₃. In all cases completely different isocoumarin derivatives were obtained. These unusual isocoumarin derivatives were isolated and characterized and their formation mechanisms are discussed. The homophthalic acid monomethyl ester was converted into the corresponding isocyanate. Reaction of the isocyanate with different amines produced the urea derivatives. Base-supported condensation reactions of these products gave first an indolinone derivative, which underwent further intermolecular condensation to give substituted indole derivatives. However, when the condensation reaction was carried out in the presence of acetic anhydride, the intermolecular reactions were suppressed. This methodology opens up a new way of synthesizing of various five-membered ring substituted indole derivatives.