Trialkylphosphonium Oxoborate as C(sp 3 )-H Oxyanion Hole Catalyst for Diels-Alder Reaction.

We have developed a catalytic protocol for Diels-Alder reaction using trialkylphosphonium oxoborates as oxyanion hole catalysts. The reaction can be operated under ambient conditions. Dienes could easily polymerize under acidic condition. Nonetheless, these acid-sensitive substrates are compatible with the catalytic protocol and the reaction scope covers a wide range of substrates.