Asymmetric Rh(I)-Catalyzed Intramolecular [3 + 2] Cycloaddition of 1-Yne-vinylcyclopropanes for Bicyclo[3.3.0] Compounds with a Chiral Quaternary Carbon Stereocenter and Density Functional Theory Study of the Origins of Enantioselectivity

A highly enantioselective Rh(I)-catalyzed intramolecular [3 + 2] cycloaddition of 1-yne-VCPs to bicyclo[3.3.0] compounds with an all-carbon chiral quaternary stereocenter at the bridgehead carbon was developed. DFT calculations of the energy surface of the catalytic cycle (complexation, cyclopropane cleavage, alkyne insertion, and reductive elimination) of the asymmetric [3 + 2] cycloaddition reaction indicated that the rate- and stereo-determining step is the alkyne-insertion step. Analysis of the alkyne-insertion transition states revealed that the serious steric repulsion between the substituents in the alkyne moiety of the substrates and the rigid H(8)-BINAP backbone is responsible for not generating the disfavored [3 + 2] cycloadducts.