CBS Catalyst
Definition and meaning of CBS Catalyst in chemistry.
CBS catalyst (Corey–Bakshi–Shibata catalyst) is a chiral oxazaborolidine that catalyzes the highly enantioselective reduction of prochiral ketones to secondary alcohols using a borane reagent as the stoichiometric reductant.
In more detail
The catalyst, derived from proline via diphenylprolinol, activates borane by coordinating it at its ring nitrogen while its boron atom binds the ketone oxygen, arranging both reactants in a rigid six-membered transition state that delivers hydride to one specific face of the carbonyl carbon. Choosing the (R)- or (S)-configured catalyst controls which enantiomer of alcohol product predominates. Developed by E. J. Corey with Raman Bakshi and Shibasaki (Shibata) in 1987, it earned Corey part of the 1990 Nobel Prize recognition for synthetic methodology and remains a workhorse for making chiral alcohol intermediates in pharmaceutical and natural-product synthesis.
Key facts
| Formula | C17H18BNO (B-methyl-CBS-oxazaborolidine) |
|---|---|
| Named after | E. J. Corey, Raman Bakshi, Shibasaki (Shibata) |
| Reaction | Catalytic asymmetric ketone reduction with borane |
| Field | Organic Chemistry |
Treating acetophenone with catalytic (S)-CBS catalyst and borane-tetrahydrofuran complex reduces the ketone to (R)-1-phenylethanol in high yield and high enantiomeric excess.
Frequently asked questions
What does CBS stand for?
Corey–Bakshi–Shibata, the chemists who reported the catalyst in 1987.
Why is the CBS reduction useful?
It converts simple prochiral ketones into single-enantiomer alcohols with only catalytic amounts of a chiral reagent, which is far more efficient than using stoichiometric chiral reducing agents.