SOLVENT AND SALT EFFECT IN PERICYCLIC-REACTIONS .10. INTRAMOLECULAR ENE REACTIONS VS COMPETITIVE PERICYCLIC PROCESSES - THE EFFECT OF SOLVENTS AND SALTS ON THE REACTION OF BROMO-2-(3-METHYL-2-BUTENYLOXY)BENZYLIDENE-MALONIC ACID DIMETHYL ESTER

The reactivity of bromo-2-(3-methyl-2-butenyloxy)benzylidene-malonic a cid dimethyl ester (3) was studied in several reaction media. In aprot ic solvents intramolecular ene reaction (IER) occurred to give cis and trans chroman derivatives (4) and (5), and some kinetic determination s were performed. In protic solvents, besides IER adducts, the product s of intramolecular hetero-Diels-Alder reaction and Claisen rearrangem ent (10 and 12 respectively) were obtained. In strong protic media, de allylation occurs to give the chromen-2-one derivative (6). Finally, t he reaction was investigated in acetonic solutions of inorganic perchl orate (barium, lithium, magnesium, and sodium), and these conditions e nhanced chemo- and stereo-selectivity and increased the rate. The kine tic effect was dramatic for magnesium perchlorate.