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 ...