LITHIUM PERCHLORATE CATALYSIS OF THE HETERO-DIELS-ALDER REACTION - A SPECIFIC LITHIUM CATION EFFECT

The lithium perchlorate catalysis of the hetero Diels-Alder reaction between 1-phenyl-4-benzylidene-5-pyrazolone and ethyl vinyl ether was kinetically investigated in five solvents. The rate increases as the salt concentration increases and a linear relationship between the relative rate and the molar fraction of the salt can be obtained. All correlations converge on a single value and this strongly supports the presence of a catalysis promoted by the lithium cation acting as a Lewis acid. The nature of the interaction between the catalyst and the solvent was also investigated.