2-Halogenoimidazolium salt catalyzed aza-Diels-Alder reaction through halogen-bond formation.

2-Halogenoimidazolium salts are found to catalyze aza-Diels-Alder reaction of aldimines with Danishefsky diene in an efficient manner. Comparative studies and titration experiments support the formation of halogen bonding between imines and catalysts.