Selective Functionalization of Aminoheterocycles by a Pyrylium Salt

Abstract The functionalization of aminoheterocycles by using a pyrylium tetrafluoroborate reagent (Pyry‐BF 4 ) is presented. This reagent efficiently condenses with a great variety of heterocyclic amines and primes the C−N bond for nucleophilic aromatic substitution. More than 60 examples for the formation of C−O, C−N, C−S, or C−SO 2 R bonds are disclosed herein. In contrast to C−N activation through diazotization and polyalkylation, this method is characterized by its mild conditions and impressive functional‐group tolerance. In addition to small‐molecule derivatization, Pyry‐BF 4 allows the introduction of functional groups in a late‐stage fashion to furnish highly functionalized structures.