Synthesis of (E)-3-Alkylidene-1-pyrrolines by the Rhodium- Catalyzed Cyclization of Terminal Alkynes with Homopropargylic Amines

The cyclization of terminal alkynes with homopropargylic amines in the presence of a rhodium complex as catalyst leads to the formation of E3alkylidene1pyrrolines. The reaction tolerates a wide range of functional groups on the terminal alkynes. The formation of a vinylidenerhodium complex, followed by the intermolecular nucleophilic attack of a homopropargylic amine nitrogen on the αcarbon atom of the vinylidenerhodium complex, is proposed as a key step in the catalytic reaction.