A One-Pot Procedure for the Regiocontrolled Synthesis of Allyltriazoles via the Pd-Cu Bimetallic Catalyzed Three-Component Coupling Reaction of Nonactivated Terminal Alkynes, Allyl Carbonate, and Trimethylsilyl Azide

A one-pot procedure for the regiocontrolled synthesis of both 2-allyl- and 1-allyl-1,2,3-triazoles via the three-component coupling (TCC) reaction between nonactivated terminal alkynes, allyl carbonate, and trimethylsilyl azide (TMSN₃) under a palladium and copper bimetallic catalyst has been developed. To accomplish the regioselective synthesis of the allyltriazoles, proper choice of two different catalyst systems is needed. The combination of Pd₂(dba)₃·CHCl₃-CuCl(PPh ₃)₃-P(OPh)₃ catalyzes the formation of 2-allyl-1,2,3-triazoles, while the combination of Pd(OAc)₂-CuBr ₂-PPh₃ promotes the formation of 1-allyl-1,2,3-triazoles. The cooperative activity of palladium and copper catalysts plays an important role in the present transformations. Most probably, the palladium catalyst works as a catalyst for generating reactive azide species, π-allylpalladium azide complex and allyl azide. The copper catalyst probably behaves as an activator of the C-C triple bond of the starting terminal alkynes by forming a copper-acetylide intermediate and thereby promotes the [3 + 2]-cycloaddition reaction between the reactive azide species and the copper-acetylide to form the triazole framework.