Solvent effects on the kinetics and diastereoselectivity of the intermolecular hetero Diels-Alder reaction of an enamino ketone with isopropenyl methyl ether under high pressure

The intermolecular hetero Diels-Alder reaction of enamino ketone 1 with isopropenyl methyl ether 2 leading to the diastereomeric products 3 and 4 is studied under high pressure up to 5 kbar and at temperatures between 30 degrees C and 120 degrees C. The kinetics are measured by on-line FT-IR spectroscopy up to 3 kbar. The ratio of the diastereomeric products is determined by HPLC-analysis. In order to gauge the influence of solvent properties on the kinetics and diastereoselectivity, the cycloaddition Is carried out in dichloromethane, in acetonitrile and in a mixture of heptane/isodurene (2:1). Clear effects of solvent polarity on the rate coefficients as well as on the activation parameters are observed. To quantify the solvent influence on the activation volume, an estimate of the intrinsic (solvent-independent) contribution to the activation volume, Delta Vintr(not equal), is made.