Selective Functionalization of Aminoheterocycles by a Pyrylium Salt

The functionalization of aminoheterocycles by using a pyrylium tetrafluoroborate reagent (Pyry-BF4) 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-SO2R 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-BF4 allows the introduction of functional groups in a late-stage fashion to furnish highly functionalized structures.