much slower than the CBS catalyzed reduction, the side reaction still presents a potential challenge to optimize stereoselectivity. In 2012, Mahale et al. developed a safe and inexpensive procedure for asymmetric reduction of ketones using in situ prepared N,N-diethylaniline-borane and oxazaborolidine catalyst from sodium borohydride, N,N-diethylaniline hydrochloride and (S)-α,α-diphenylprolinol Variations Although CBS catalyst 1 developed by Corey has become commonly employed in the CBS reduction reaction, other derivatives of the catalyst have been developed and utilized successfully. The R’ group of the CBS catalyst plays an important role in the enantioselectivity of the reduction, and as illustrated in above in the Scope section, several variations of the CBS R’ group have been employed to optimize selectivity. Applications Over the past couple of decades, the CBS reduction has gained significant synthetic utility in the synthesis of a significant number of natural products, including lactones, terpenoids, alkaloids, steroids, and biotins. The enantionselective reduction has also been employed on large scale in industry. Jones et al. utilized the CBS reduction in the total synthesis of MK-0417, a water-soluble carbonic anhydrase inhibitor which has been used therapeutically to reduce intraocular pressure. Asymmetric reduction of a key bicyclic sulfone intermediate was accomplished with the CBS oxazaborolidine catalyst containing Me as the R’ group. Asymmetric reduction of a 1,1,1-trichloro-2-keto compound is the first stage of the Corey–Link reaction for synthsis of amino acids and related structures with a choice of either natural or un-natural stereochemistry and various side-chains. Asymmetric reduction of 7-(Benzyloxy)hept-1-en-3-one leads to (S)-7-(Benzyloxy)hept-1-en-3-ol, a chiral alcohol that leads directly to synthesis of kanamienamides, that are currently researched as enamide containing enol ethers that show potent inhibition of cancer cells. The selective formation of the chiral product is achieved by (R)-CBS catalyst with 89% yield and with 91% enantiomeric excess. See also Midland Alpine borane reduction Noyori asymmetric hydrogenation References Name reactions Organic reduction reactions