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.