Copper-Catalyzed Cycloaddition between Secondary Phosphine Oxides and Alkynes: Synthesis of Benzophosphole Oxides

Benzophosphole derivatives have attracted significant attention as promising organic optoelectronic materials. We have successfully developed a copper (2 mol%)/ tert-butyl hydroperoxide (2 equiv.) catalyst system for reaction of readily available secondary phosphine oxides and alkynes in acetonitrile at 60 degrees C under air, which provides a rapid access to a structurally diverse array of benzophosphole oxides in moderate to good yields within 30 min. The method can be easily used for a large-scale preparation. Preliminary mechanistic studies revealed that the addition of a phosphoryl radical onto a triple bond followed by cyclization on the phenyl moiety of the secondary phosphine oxide might occur to form the benzophosphole oxide.