Rhodium-Catalyzed Enantioselective Silylation of Cyclopropyl C-H Bonds.

Hydrosilyl ethers, generated in situ by the dehydrogenative silylation of cyclopropylmethanols with diethylsilane, undergo asymmetric, intramolecular silylation of cyclopropyl C-H bonds in high yields and with high enantiomeric excesses in the presence of a rhodium catalyst derived from a rhodium precursor and the bisphosphine (S)-DTBM-SEGPHOS. The resulting enantioenriched oxasilolanes are suitable substrates for the Tamao-Fleming oxidation to form cyclopropanols with conservation of the ee value from the C-H silylation. Preliminary mechanistic data suggest that C-H cleavage is likely to be the turnover-limiting and enantioselectivity-determining step.