Synthesis of Dibenzophospholes by Tf2O-Mediated Intramolecular Phospha-Friedel-Crafts-Type Reaction.

A Tf2O-mediated intramolecular phospha-Friedel-Crafts-type reaction of secondary biarylphosphine oxides has been developed. The reaction is promoted simply by Tf2O to form the corresponding dibenzophospholes under metal-free conditions. The starting substrates are readily available and easy-to-handle phosphine oxides, and the regioselectivity is controlled by the innate electronic nature. Thus, this newly developed protocol can provide concise and complementary approach to the highly π-conjugated dibenzophospholes of potent interest in material chemistry.