SOLVENT EFFECTS ON ENDO EXO-SELECTIVITIES AND REGIO-SELECTIVITIES OF DIELS-ALDER REACTIONS OF CARBONYL-CONTAINING DIENOPHILES/

The selectivity of Diels-Alder reactions of methyl vinyl ketone and me thyl acrylate, with cyclopentadiene and isoprene, have been studied in 18 pure solvents and aqueous mixtures. The results obtained have been analysed by means of regression models, using empirical solvent param eters. The endo/exo selectivity mainly depends on the solvophobic (S-p ) and hydrogen bond donor (alpha) properties of the solvent. The influ ence of the dipolarity (pi) is only observed in the reactions with me thyl acrylate. Regioselectivity almost exclusively depends on the hydr ogen bond donor ability of the solvent. The double coordination observ ed with highly hydrogen bond donating solvents in the case of methyl v inyl ketone greatly increases the para/meta isomer ratio.