Iminium ion catalysis: Use of the α-effect in the acceleration of the Diels–Alder reactionElectronic supplementary information (ESI) available: 1H NMR, 13C NMR, IR and MS spectra. See http://www.rsc.org/suppdata/cc/b2/b212239a/

The alpha-effect can be used in the acceleration of the Diels-Alder reaction between a series of dienes and electron deficient dienophiles using iminium ion catalysis, providing a novel molecular scaffold capable of performing this class of catalytic process.