New insights on the mechanism of the transition-metal stereoselective olefin cyclopropanation.

We have carried out a theoretical analysis of the intermolecular cyclopropanation of propargylic esters with alkenes. DFT calculations allow us to propose a reaction mechanism, and provide explanations for the reasons behind the difference between the inter- and intramolecular versions of this process. The results strongly suggest that the entropic effects could modulate the operative mechanism and account for the mechanistic discrepancy. The calculated model also justifies the experimental stereoselectivity on the basis of intra- and intermolecular interactions. In addition, we have taken into account other transformations of propargylic carboxylates catalyzed by late transition metals, and the results rationalize the accumulated experimental observations.