(S)-Me-CBS Catalyst

Technical Specifications

Product Description & Scientific Applications

(S)-Me-CBS Catalyst (also called (S)-Corey’s catalyst) is the chiral oxazaborolidine used in the Corey–Bakshi–Shibata (CBS) reduction of ketones. Borane first coordinates to the catalyst’s Lewis basic ring nitrogen, which enhances the Lewis acidity of the endocyclic boron atom that then activates the ketone for hydride transfer.

Enantiofacial selectivity in the reduction requires effective discrimination between the large and small substituents flanking the prochiral carbonyl carbon.

Substrate scope

• Aryl alkyl ketones: Reduces prochiral aryl alkyl ketones, exemplified by the acetophenone-to-1-phenylethanol reaction used as the standard benchmark for enantioselectivity.
• α,β-Ynones: Performs the first catalytic enantioselective reduction of α,β-ynones with catecholborane, giving propargylic alcohols.
• Keto oxime ethers (C=N): Converts keto oxime ethers to cyclic (1S,2R)-cis amino alcohols via oxazaborolidine/borane catalysis.
• N-protected 2-amino-1-arylethanones: Asymmetric borane reduction with a borane/N-ethyl-N-isopropylaniline hydride source gives chiral amino alcohol precursors.
• Keto acetals: Reduced to chiral hydroxy acetals in up to 100% ee using BH3·PhNEt2 as the hydride source.

Mechanistic studies

• Steric kinetic isotope effects have been applied with the oxazaborolidine catalyst to quantitatively probe the steric interactions that govern stereoselection in the CBS reduction transition state.
• In one reported synthesis, a CBS-oxazaborolidine reduction gave a product whose enantiomeric excess was determined by chemical methods and whose structure was confirmed by X-ray crystallography.

Shipping Destinations

• EU & UK: Priority delivery, 2–5 business days.
• United States (DDP): 3–7 business days, duties and taxes prepaid.
• EFTA Countries (DDP): 3–7 business days, duties and taxes prepaid.
• Worldwide: 7–14 business days, selected locations.