Highly Efficient Intra- and Intermolecular [4 + 2] Cycloaddition Reaction Catalyzed by Rhodium Complex

A cationic Rh(Ι) complex, [(η6-C10H8)Rh(cod)]BF4, has been found to be a quite useful catalytic system for both the intermolecular [4 + 2] cycloaddition reaction of 1,3-dienes with nonactivated acetylenes and the intramolecular [4 + 2] cycloaddition of dienyne under very mild reaction conditions (CH2Cl2, 15 °C, 15 min).