CBS catalysts
CBS catalysts or Corey-Bakshi-Shibata catalysts are chiral catalysts and derivatives of the natural amino acid ( S ) -proline . It was named after the chemists E. J. Corey , S. Shibata and RK Bakshi , who developed it. CBS catalysts are chiral molecules that cause certain chemical reactions to occur enantioselectively . This is achieved in that one of the two possible enantiomers is preferentially formed in the transition state due to lower steric tension .
CBS catalysts are used as a chiral auxiliary in CBS reduction , the Diels-Alder reaction and the [3 + 2] cycloaddition .
Chemical structure
The CBS reagent is a boronic acid ester amide of a proline derivative, from which the chiral information originates. The structure is stiffened by the two phenyl radicals in the side chain of the asymmetrically substituted carbon atom and the degrees of freedom of rotation are reduced.
presentation
It is represented from the enantiomerically pure amino acid ( S ) -proline or a proline derivative. First, the amino group of the proline is provided with a benzyloxycarbonyl protective group (Cbz, Z protective group). Then the carboxylic acid is converted to the methyl ester . A Grignard reaction with phenylmagnesium chloride then leads to the tertiary alcohol. The splitting off of the protective group and subsequent reaction with methyl boronic acid finally leads to the CBS reagent.
literature
- S. Itsuno, K. Ito, A. Hirao, S. Nakahama: Asymmetric reduction of aromatic ketones with the reagent prepared from (S) - (-) - 2-amino-3-methyl-1,1-diphenylbutane-1- ol and borane . In: J. Chem. Soc., Chem. Commun. . 8, 1983, p. 469. doi : 10.1039 / c39830000469 .
- Elias J. Corey, S. Shibata, RK Bakshi: An efficient and catalytically enantioselective route to (S) - (-) - phenyloxirane . In: J. Org. Chem. . 53, 1988, pp. 2861-2863. doi : 10.1021 / jo00247a044 .
- EJ Corey, Takanori Shibata, and Thomas W. Lee: Asymmetric Diels-Alder Reactions Catalyzed by a Triflic Acid Activated Chiral Oxazaborolidine . In: J. Am. Chem. Soc. . 124, No. 15, 2002, pp. 3808-3809. doi : 10.1021 / ja025848x .