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(S)-(-)-alpha,alpha-Diphenylprolinol is used to prepare the corresponding oxazaborolidines for the borane-mediated asymmetric reduction of ketones.
Precursor of Corey, Bakshi and Shibata's oxazaborolidine derivatives (CBS catalysts) for enantioselective reduction of prochiral ketones: J. Am. Chem. Soc., 109, 5551 (1987). Ketones are not reduced rapidly by either borane-THF or the oxazaborolidine alone but together they form a complex which reduces ketones rapidly and stereoselectively, permitting reduction with very high ee in the presence of a catalytic amount of the oxazaborolidine: J. Am. Chem. Soc., 109, 7925 (1987).
For use in conjunction with borane generated in situ using NaBH4 and iodine, see: Tetrahedron, 50, 6411 (1994). For an optimized in situ procedure for generation and use of the oxazaborolidine from BMS, see: Tetrahedron: Asymmetry, 7, 3147 (1996). In a comparison with other oxazaborolidine precursors, diphenylprolinol gave the best results (same ref.). For in situ generation of an asymmetric reduction system using trimethyl borate and BMS, see: Synlett, 273 (1997). For the generation and use of the phenyl oxazaborolidine, using Benzeneboronic acid, A14257, see: Tetrahedron Lett., 31, 7415 (1990); 32, 7175 (1991); J. Org. Chem., 57, 7115 (1992). For a detailed comparative study of various alkyl- and aryl-substituted borolidines, see: J. Org. Chem., 56, 763 (1991). For a process for the in situ formation of butyl oxazaborolidines using 1-Butylboronic acid, A13725, see: Tetrahedron Lett., 33, 4141 (1992). For use for the catalytic enantioselective synthesis of chiral monosubstituted oxiranes, see: Tetrahedron Lett., 34, 5227 (1993).
For reviews of oxazaborolidines as enantioselective catalysts, see: Angew. Chem. Int. Ed., 31, 729 (1992); 37, 1986 (1998); Tetrahedron: Asymmetry, 3, 1475 (1992). For reviews of the asymmetric reduction of ketones, see: Synthesis, 605 (1992); Chem. Ind. (London), 552 (1994).
See also the preformed catalyst (S)-2-Methyl-CBS-oxazaborolidine, L14583, and (S)-2-Methyl-CBS-oxazaborolidine monohydrate, L09219.
Gefahrenhinweise (EU): H315-H319-H335
Causes skin irritation. Causes serious eye irritation. May cause respiratory irritation.
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