ChemInform Abstract: Lewis Acid Catalysis of a Diels‐Alder Reaction in Water.

Abstract

1996 cycloaddition reactions cycloaddition reactions O 0070 -051Lewis Acid Catalysis of a Diels-Alder Reaction in Water.-The effect of Co2+, Ni2+, Cu2+, and Zn2+ ions as Lewis acid catalysts on the rate and endo-exo selectivity of the Diels-Alder reaction between the bidendate dienophiles (I) and cyclopentadiene in water is studied. The reaction is accelerated greatly by Lewis acid catalysis combined with an aqueous solvent effect. The kinetics of the catalyzed reaction are analyzed in terms of equilibrium constants for complexation of the Lewis acid with (I) and rate constants for the reaction of the resulting complexes with cyclopentadiene. The rate enhancing effect of water on the catalyzed reaction is less pronounced than the corrresponding effect on the uncatalyzed reaction and the increase of the endo-exo selectivity induced by water in the uncatalyzed process is completely absent for the Lewis acid catalyzed reaction. -(OTTO, S.; BERTONCIN, F.; ENGBERTS, J.