Metal-Free Electrophilic Phosphination/Cyclization of Alkynes

A metal-free electrophilic phos­phin­ation reaction has been developed. Electro­philic phosphorus species generated in situ from secondary phos­phine oxides and Tf2O smoothly couple with alkynes possessing pendant nucleo­philes to afford the corresponding phos­phin­ated cyclization products in good yield. Preliminary NMR studies show that phos­phir­enium species may be involved as inter­mediates of the cyclization reactions.