Tandem One-Pot Synthesis of Polysubstituted NH-Pyrroles Involving the Palladium-Catalyzed Intramolecular Oxidative Amination of the Zinc Bromide Complex of β-Enamino Esters.

The Pd-catalyzed oxidative olefin amination of the zinc bromide complex intermediate, formed by the sequential reaction of nitriles with a Reformatsky reagent and 1-alkynes, affords pyrrole derivatives in good to excellent yields. This tandem protocol provides a simple, efficient, and atom- and pot-economical way to quickly build polysubstituted NH-pyrroles starting from readily available reagents in a regiocontrolled manner with a broad substrate scope and high functional group tolerance. In contrast, the Pd-catalyzed oxidative olefin amination of an isolated α-vinyl-β-enamino ester did not proceed effectively, but the reaction efficiency can be restored by addition of n-BuZnBr or Zn(OAc)2, indicating the crucial role of the zinc complex in this transformation. The synthetic utility of this protocol is exemplified by the rapid synthesis of pyrrolophenanthrenes and pyranopyrrolones through selective Pd- and Cu-catalyzed C-C and C-O bond-forming reactions. [ABSTRACT FROM AUTHOR]