A mild catalytic system for radical conjugate addition of nitrogen heterocycles† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc00243b Click here for additional data file.

Pyridines and diazines are critical structural elements in many biologically active small molecules and, as a result, signicant research effort has been devoted to their preparation. In addition to de novo heterocycle assembly, a number of powerful methods exist for the functionalization of these heteroarenes. For example, Minisci radical addition is a direct and effective synthetic approach to the preparation of alkyl pyridines and diazines, however, the regiochemical outcome of these processes is largely dictated by the inherent reactivity of a given substrate (or substrate class). Catalytic coupling processes of halogenated heteroarene substrates with alkyl metals and, more recently, alkyl halides have been developed for the direct synthesis of alkylated heteroaromatics. We recently became interested in developing an alternative approach to complex pyridine and diazine synthesis via direct union of these heteroaromatic units with alkenes. More specically, we envision a general strategy for programmed, regiospecic heteroarene activation that functions through heteroaryl radical intermediates. In contrast to alkyl radicals, aryl radical species effectively engage a wide range of unsaturated substrates. Consequently, mild conditions that deliver these reactive intermediates could enable the development of many discrete, practical processes for complex pyridine and diazine synthesis (Fig. 1). Here, we describe the development of a catalytic system for heteroaryl radical formation and direct coupling with electrondecient alkenes, a reductive Meerwein arylation process (illustrated in Fig. 1). Conjugate addition is a highly utilized strategic disconnection, but direct Michael addition of 6-membered nitrogen heterocycles remains challenging. Because pyridines are weakly nucleophilic, they require activation to effectively add to alkenes. Miyaura demonstrated that rhodium-catalyzed asymmetric conjugate addition of o-methoxy