The modulation of face–face π–π interactions in Lewis acid catalysis

The enantiomeric excess observed for the exo-adduct from the Lewis acid catalysed Diels–Alder reaction between cyclopentadiene and methacrolein can be increased up to 21% by simple modification of the electronics of the aromatic ring in a series of stilbene-derived diol ligands, suggesting that the proposed face–face π–π interaction between the catalyst and the dienophile can be modulated by altering the electron density on the aromatic ring.