Palladium-Catalyzed Three-Component Reaction of Propargyl Carbonates, Isocyanides, and Alcohols or Water: Switchable Synthesis of Pyrroles and Its Bicyclic Analogues

In the presence of a catalytic amount of Pd(OAc)2 and a stoichiometric amount of tert-butylamine, the reaction of propargyl carbonates, isocyanides, and alcohols afforded polysubstituted aminopyrroles in good yields. Using water as a nucleophile instead of alcohol, the same reaction provided 1,4-dihydro-6H-furo[3,4-b]pyrrol-6-imines. A triple isocyanide insertion to the hypothetic (σ-allenyl)palladium(II) intermediate was involved in these ABC3-type multicomponent reactions. The key role of tert-butylamine was accounted for by its reaction with in situ generated carbon dioxide to form the carbamic acid, which in turn served as a nucleophile to trap the nitrilium intermediate.