The evolution of organic synthesis relies heavily on the design and discovery of new reactions that generate structural complexity and value with step economy.1 Toward this end, we previously reported studies on new [4+4],2 [4+2],3 [5+2],4 and [6+2]5 cycloadditions and novel three-component [2+2+1],6 [4+2+1],6 and [5+2+1]7 reactions.8 In the course of our studies on the Rh-(I)-catalyzed dienyl Pauson-Khand [2+2+1] reaction, we observed that diene-ynes react significantly faster than alkene-ynes to produce cyclopentenone products. This enhanced reactivity suggests that dienes might be used instead of alkynes to effect a [2+2+1] reaction with simple alkenes and CO. Conventional Pauson-Khand reactions and more recent catalyzed variants have been limited almost exclusively to the use of alkynes as one of the two carbon components.9,10 Bis-alkenes do not undergo this three-component reaction, although useful alternative two-step stoichiometric processes have been reported in which a preformed metallacycle is converted with CO to a cyclopentanone.11 We report herein the first examples of a metal-catalyzed [2+2+1] reaction involving a diene, an alkene, and CO.1
