In recent years the identification of new transformations and modes of reaction for iminium ion catalysis has attracted much interest, but the majority of reports have not looked at understanding the often complex processes taking place within the reaction flask. We have sought to understand these reactions and to test the validity of computational models. Iminium ion catalysts can be used to accelerate a variety of cycloaddn. and conjugate addn. processes. The accepted catalytic cycles do not help in explaining important observations, particularly regarding reaction medium. Through exptl. and theor. investigations we have focussed on three principle observations for the Diels-Alder cycloaddn.: - Water increases the rate of reactions. - Water increases the e.e. of the isolated products. - Theor. models for the conformations of the active species do not agree. We present evidence offering insights into the crucial roles of water within these transformations
