Enantioselective Catalytic Cyclopropanation-Rearrangement Approach to Chiral Spiroketals
Kuioyng Dong1, Raj Gurung1, Xinfang Xu2
1Department of Chemistry, University of Texas at San Antonio, San Antonio, Texas 78249, United States.
Abstract:
A highly enantioselective synthesis of chiral heterobicyclic spiroketals is reported via a "one-pot" cyclopropanation-rearrangement (CP-RA) cascade reaction that is sequentially catalyzed by a chiral Rh(II) catalyst and tetrabutylammonium fluoride (TBAF). Exocyclic vinyl substrates form spirocyclopropanes with tert-butyldimethylsilyl-protected enoldiazoacetates in excellent yields and with excellent enantioselectivities when catalyzed by chiral dirhodium(II) carboxylates, and following desilylation with simultaneous rearrangement in the presence of TBAF, they give (S)-spiroketals in high yields with excellent chirality retention (>95% ee).
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