Theoretical studies on the mechanism of Rh-catalyzed [(3+2+2)] cycloisomerization reactions of dienophile-substituted alkylidenecyclopropanes

Abstract

The detailed reaction mechanism of Rh-catalyzed [(3+2+2)] cycloisomerization reactions of dienophile-substituted alkylidenecyclopropanes to construct the bridged tricyclic products with DFT calculations has been investigated. The catalytic cycle primarily comprises four steps: oxidative addition, proximal alkene insertion, distal alkene insertion, and reductive elimination. The reactions initiate with Rh-mediated the cleavage of cyclopropane distal C−C bond to give the key η⁴-TMM Rh(III) intermediate, which undergoes the proximal alkene insertion step to dictate the stereochemical outcome. The subsequent competing the 1,2-insertion and 2,1-insertion of the distal alkene moiety has also been discussed for comparison. The calculations reproduce quite well diastereoselectivity observed experimentally, demonstrating that the cis coordination pathway has high diastereocontrol. For comparison, various C−C coupling reaction pathways and substrate scopes have been examined.