SOLVENT EFFECTS ON DIELS-ALDER REACTIONS - THE USE OF AQUEOUS MIXTURES OF FLUORINATED ALCOHOLS AND THE STUDY OF REACTIONS OF ACRYLONITRILE

Rate, endo/exo, regio- and diastereo-facial selectivities of several D iels-Alder reactions were measured in a series of fluorinated alcohol- water mixtures, whose solvophobicity has been determined by means of t he solvophobic power (Sp) parameter. Solvophobicity is the main factor influencing the reaction rate, although in some reactions hydrogen bo nd donating (HBD) ability may also playa role. Both solvophobicity and HBD ability are important to account for changes in endo/exo selectiv ity. HBD ability is the main factor responsible for the changes in reg io- and diastereo-facial selectivities, induced by the reaction medium . On the other hand, the kinetic late constants and endo/exo selectivi ty of the reaction of acrylonitrile with cyclopentadiene, as well as t he regioselectivity of the reaction of acrylonitrile with isoprene, ha ve been determined in 23 reaction media. The analysis of the results u sing empirical solvent parameters show that the reaction rate depends on solvophobic, HBD and dipolarity interactions,whereas endo/exo selec tivity is influenced by solvophobic and dipolarity interactions, and t he regioselectivity only by HBD effects.