Mechanistic Insights into Cyclopropenes-Involved Carbonylative Carbocyclization Catalyzed by Rh(I) Catalyst: A DFT Study.

Computational studies were carried out to provide mechanistic insights into the Rh(I)-catalyzed activation of cyclopropenes and the detailed mechanistic pathways of [3+2+1] carbonylative carbocyclization of tethered ene- and yne-cyclopropenes. Computational results suggest that it is more favorable for the cyclopropene moiety of tethered ene-cyclopropenes to initially undergo heterolytic cleavage of a C-C σ-bond to form a vinyl Rh(I) carbenoid intermediate than to proceed through homolytic C-C σ-bond cleavage to generate a rhodacyclobutene intermediate. The yielded vinyl Rh(I) carbenoid intermediate could undergo cyclization to generate a Rh(III) metallacyclobutene intermediate, which could further lead to a thermodynamically more stable six-coordinated Rh(III) metallacycle intermediate in the presence of additional CO. Afterward, it is more feasible for the yielded six-coordinated Rh(III) metallacycle to sequentially undergo CO migratory insertion, cyclization, and reductive elimination to furnish the final cyclohexenone product. The origin of stereoselectivity of the product was also discussed. The proposed mechanistic pathway can also be applied to the Rh(I)-catalyzed carbonylative carbocyclization of tethered yne-cyclopropenes and vinyl cyclopropenes to produce phenol derivatives. The main mechanistic difference for the vinyl cyclopropene substrate is that the conversion of Rh(I) carbenoid intermediate to the Rh(III) metallacycle proceeds via intramolecular 6π electrocyclization.