Solvent effects on endo/exo- and regio-selectivities of Diels–Alder reactions of carbonyl-containing dienophiles

Abstract

The selectivity of Diels–Alder reactions of methyl vinyl ketone and methyl 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 parameters. The endo/exo selectivity mainly depends on the solvophobic (S_p) and hydrogen bond donor (α) properties of the solvent. The influence of the dipolarity (π*) is only observed in the reactions with methyl acrylate. Regioselectivity almost exclusively depends on the hydrogen bond donor ability of the solvent. The double coordination observed with highly hydrogen bond donating solvents in the case of methyl vinyl ketone greatly increases the para/meta isomer ratio.