NMR AND AM1 STUDY OF THE TAUTOMERIC EQUILIBRIUM OF ISOCHROMAN-1,3-DIONES

Reaction of homophtalic anhydrid with aliphatic or aryl anhydrids (or acid chlorides) and an appropriate base gives 4-acyl and 4-aroylisochr oman-1,3-diones. The structure of these isochroman-1,3-diones was dete rmined by H-1, C-13 and O-17 NMR spectrometry. In solution, among the three possible tautomers, only the enolic one with exocyclic double bo nd was observed. These results are in good agreements with AM1 calcula tions ones.