Coinage (Au, Ag, Cu) metal-catalyzed (3 + 2) annulation of α-aminoketones and electron-deficient alkynes as a route to 3-EWG-substituted pyrroles

Abstract

Coinage (Au, Ag, Cu) metal-catalyzed (3 + 2) annulation of α-aminoketones and electron-deficient alkynes provides a modular one-step route to a variety of 3-EWG-substituted pyrroles. Apart from gold(I) complexes, which “open any door” and catalyze the annulation regardless of the identity of the alkyne EWGs [–SO₂R, –CO₂R, –PO(OR)₂], the other cheaper coinage metal (first of all Cu, but also Ag) species function as alternative catalysts for the selective activation of alkynylsulfones and their conversion to 3-sulfonylpyrroles. The developed catalytic annulation operates under relatively mild conditions (5 mol% of a coinage metal catalyst, DCE, 80 °C) and provides a high functional group tolerance (36 examples; yields up to 99%). The synthetic utility of the obtained products was illustrated by practical post-modification of either the pyrrole backbone, or the peripheral substituents.