Intermolecular Cyclization between Carboranylphosphines and Electron-Deficient Alkynes

An efficient and facile method to synthesize zwitterionic nido-carborane-fused five-membered P-heterocycles was developed. Intermolecular cyclization between carboranylphosphines and electron-deficient alkynes occurred at 50 °C in THF, affording the products with up to 82% yield. For unsymmetrical alkynes, the more electrical-deficient site is selectively connected to phosphorus in the products. Structures of three products have been confirmed by X-ray diffraction analysis of single crystals. The key step of the reaction is believed to be deprotonation of acidic C–H of carborane by the alkenyl anion derived from addition of carboranylphosphines to alkynes.