Cationic Rhodium(I)-Catalyzed Carbonylative [2+2+1] Cycloaddition of Diynes

We describe Rh(I)-catalyzed carbonylative [2+2+1] cycloaddition reactions of diynes with CO to give cyclopentadienone derivatives (CPDs). Previous reports on the use of neutral rhodium(I) complexes, such as [RhCl(cod)]₂ and RhCl(PPh₃)₃, indicate that no CPD products are formed or that they are produced in low yields, even at elevated temperatures. The reaction described herein, which uses a cationic rhodium(I) complex, [Rh(cod)₂]BF₄, as a catalyst, proceeds smoothly at room temperature to give cyclopentadienone derivatives. The key to this is the use the cationic rhodium(I) complex as a catalyst, which produces an additional coordination site on the rhodium for the substrate (a diyne) to approach, than neutral rhodium complexes.