Synthesis and Evaluation of Azolium‐Based Halogen‐Bond Donors

A method for the synthesis of iodinated imidazolium and triazolium N‐heterocyclic halogen‐bond‐donor catalysts has been developed. This approach was applied to the synthesis of a variety of 1,2,4‐triazolium salts to prepare a series of novel chiral halogen‐bond‐donor catalysts. The counterions of the iodinated triazoliums can be readily exchanged with chiral and achiral non‐coordinating counterions to produce unique scaffolds. Their ability to promote/catalyse a conjugate addition reaction with indole was investigated. Through these initial studies, a set of general guidelines and considerations for the application of these halogen‐bond donors in organocatalysis have been established. A method for the synthesis of N‐heterocyclic halogen‐bond donors has been developed along with an evaluation of these new species as potential catalysts. Their application in the promotion of conjugate addition reactions with indole was investigated and a set of guidelines for the use of halogen‐bond donors in organocatalysis was established.