Direct intramolecular double cross-dehydrogentive-coupling (CDC) cyclization of -(2-pyridyl)amidines under metal-free conditions

A facile transition-metal-free protocol to form 2-iminoimidazo[1, 2- a ]-pyridines bearing a -CHBr 2 group and an aza-quaternary carbon center at the 3 position from N -(2-pyridyl)amidines substrates, in which the new heterocyclic skeletons constructed from amidines via radical reactions or nucleophilic substitution reactions are promoted only by CBr 4 under mild conditions, is demonstrated. The reactions were realized by intramolecular CDC reaction involving C-N and C-C bond formation via the sequential C(sp 3 )-H bifunctionalization mode on the same carbon atom under mild conditions. Moreover, this work also provides an excellent and representative example for CBr 4 as an efficient reagent to initiate radical reactions under initiator-free conditions or to give rise to nucleophilic substitution reactions only by base. A metal-free protocol to form 2-iminoimidazo[1,2- a ]-pyridines from N -(2-pyridyl)amidines, in which the constructed heterocyclic skeletons are promoted by CBr 4 via radical or nucleophilic substitution reactions under mild conditions, is demonstrated.