Copper-Catalyzed Synthesis of Pyrrolidines and Piperidines

Significance

Reported is the synthesis of pyrrolidines 3 and piperidines 6 via a copper-catalyzed, one-pot tandem hydroamination-alkynylation sequence. Microwave heating was found to be most efficient with an increase in the reaction time from 30 minutes to 12 hours observed when using conventional heating. A wide range of acetylenes 2 were tolerated, with excellent yields observed in all cases. The synthesis of fused product 7, obtained from a proline derivative, and one example of a seven-membered ring were also presented. An intermolecular variant, albeit in low yield, possibly heralds future synthetic opportunity.