Abstract
An attempt to prepare 3-substituted isocoumarins by the condensation of acid chlorides with homophthalic acid to afford the desired 3-chloromethylisocoumarin was made but surprisingly the desired isocoumarin (8) was not formed. However, a novel 3H-furo[3,4-c]isochromene-1,5-dione (9) was isolated which was characterized by spectroscopy and X-ray crystallography. A mechanism for the formation of 3H-furo[3,4-c] isochromene-1,5-dione (9) is also proposed.