Anti-Markovnikov Addition of Both Primary and Secondary Amines to Terminal Alkynes Catalyzed by the TpRh(C2H4)2/PPh3 System

Abstract

Terminal alkynes react with secondary amines in the presence of TpRh(C2H4)2/PPh3 (Tp = trispyrazolylborate) to give anti-Markovnikov E-enamines. Both Tp and PPh3 ligands are essential for the reaction. The reaction tolerates functional groups, such as ester, nitrile, and siloxy groups, on the terminal alkynes. Primary amines also add to terminal alkynes in anti-Markovnikov fashion, yielding the corresponding imines. The formation of a vinylidene−rhodium complex followed by the intermolecular nucleophilic attack by an amine nitrogen at the α-carbon atom of the vinylidene−metal intermediate may be involved in a key step in the catalytic reaction.