Metal-Controlled Switchable Regioselective Synthesis of Substituted Imidazoles and Pyrroles Ring Opening/Cyclocondensation with 2-Azirines.

Catalytic selective annulation of 2-azirines constitutes a general and modular strategy for the generation of molecular complexity. By using Pd-catalyzed ring opening/heterocyclization associated with direct cleavage of C-N and C-C bonds under appropriate conditions, the formation of imidazoles is presented. Alternatively, the silver-catalyzed radical [3 + 2] cycloannulation of 2-azirines and 1,3-dicarbonyl compounds provides highly functionalized pyrrole derivatives. Both aliphatic cyclic and acyclic diketones are tolerated with good regioselectivity. Moreover, a radical capture experiment was carried out to determine the proposed mechanism, providing support for a facile radical process.