Synthesis of Pyridylsulfonium Salts and their Application in Transition Metal-Free Formation of Functionalized Bipyridines

An S-selective arylation of pyridylsulfides with good functional group tolerance has been developed. The resulting pyridylsulfonium salts have been used in a scalable transition metal-free coupling protocol yielding functionalized bipyridine scaffolds with extensive functional group tolerance and modularity. Pyridylsulfonium salts were coupled to lithiated pyridines in a sulfur-mediated synthesis of bipyridines. This modular methodology, permits selective introduction of functional groups from commercially available pyridyl halides, furnishing symmetrical and unsymmetrical 2,2’- and 2,3’-bipyridines. Iterative application of the methodology enabled the synthesis of a functionalized terpyridine with three different pyridine components.