A Practical Method for Asymmetric Borane Reduction of Prochiral Ketones Using Chiral Amino Alcohols and Trimethyl Borate

Masui, Masao; Shioiri, Takayuki

doi:10.1055/s-1997-779

Cited by 88 publications

(47 citation statements)

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“…Although the enantioselectivity was improved by increasing catalyst loading, this is not an economic mode, especially for large-scale preparation. 7,8 The problem needs to be solved. After optimizing the reduction conditions and investigating the effect of temperature on the enantioselectivity of the asymetric reduction, 9 we found that the enantioselectivity of alkyl 1-(4-alkythiophenyl) ketones 2 with a strong coordination of the sulfur atom to the boron atom was improved when the reduction was carried out in toluene at 25jC with 10% molar amount of the catalyst and one equivalent of borane.…”

Section: General Procedures For Asymmetric Reduction Of Ketonesmentioning

confidence: 99%

Preparation of highly optically pure homochiral sulfide‐containing alcohols via oxazaborolidine‐catalyzed asymmetric borane reduction of ketones

Wei

Xia

et al. 2004

Chirality

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Section: General Procedures For Asymmetric Reduction Of Ketonesmentioning

confidence: 99%

Preparation of highly optically pure homochiral sulfide‐containing alcohols via oxazaborolidine‐catalyzed asymmetric borane reduction of ketones

Wei

Xia

et al. 2004

Chirality

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“…7) We have also reported the efficient catalyst prepared from aluminum triethoxide 8) and DPP for asymmetric borane reduction. However, the additive, trimethyl borate or aluminum triethoxide, is necessary to prepare the catalysts in these methods.…”

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confidence: 95%

Asymmetric Borane Reduction of Prochiral Ketone Using Chiral Bis(.ALPHA.,.ALPHA.-diphenyl-2-pyrrolidinemethanol) Carbonate.

Yanagi

Kikuchi

Takeuchi

et al. 2003

CHEMICAL & PHARMACEUTICAL BULLETIN

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Several asymmetric borane reductions of prochiral ketones using a chiral oxazaborolidine catalyst prepared from a chiral b-amino alcohol have been reported. [1][2][3][4][5][6] Especially, the use of the oxazaborolidine, MeCBS or HCBS, prepared from chiral a,a-diphenyl-2-pyrrolidinemethanol (DPP) for the asymmetric borane reduction of various ketones showed high enantioselectivities ( Fig. 1). HCBS could be synthesized from DPP and a reducing reagent such as the borane-dimethyl sulfide complex (BH 3 · Me 2 S) or the borane-tetrahydrofuran complex. However, the synthesis of HCBS requires a long reaction time in tetrahydrofuran (THF).3) Masui and Shioiri reported the asymmetric reduction by BH 3 · Me 2 S using a catalyst easily generated in situ from chiral DPP and trimethyl borate. 7) We have also reported the efficient catalyst prepared from aluminum triethoxide 8) and DPP for asymmetric borane reduction. However, the additive, trimethyl borate or aluminum triethoxide, is necessary to prepare the catalysts in these methods. Mathre et al. tried to prepare a borane complex of HCBS in toluene by the same procedure used to prepare a borane complex of MeCBS (Fig. 1), but they obtained only a dimer complex.5) Salunkhe and Burkhardt reported that the complex generated from the chiral DPP and borane in toluene included the dimer complex.6) Efforts to use the dimer complex as a catalyst resulted in a low enantioselectivity for the reduction of acetophenone.In this paper, we report the asymmetric borane reduction of a prochiral ketone using a catalyst generated in situ from DPP and BH 3 · Me 2 S in various solvents. We also report that the carbonate of DPP is useful for the reduction.In our previous report, 8) we described that the asymmetric reduction of acetophenone using (S)-DPP and BH 3 · Me 2 S in THF required a long reaction time (1.5 h) after the addition of the ketone and gave (1R)-1-phenylethanol with 94.7% ee. During the reaction, immediately after BH 3 · Me 2 S was added to a solution of (S)-DPP in THF, the addition of the ketone to the solution was started. We thought that if the mixture of (S)-DPP and BH 3 · Me 2 S was stirred to prepare a catalyst for a sufficient time before the addition of the ketone, the reaction time would be shorter and the optical purity of the alcohol would be higher.First we examined the asymmetric borane reduction of acetophenone using a catalyst generated in situ from DPP and BH 3 · Me 2 S in various solvents. A catalyst solution was generated from (S)-DPP (0.5 mmol) and BH 3 · Me 2 S (5 mmol) in each solvent (5 ml) by stirring at room temperature for 1 h. A solution of acetophenone (5 mmol) in each solvent (10 ml) was then added dropwise to the catalyst solution via a syringe pump at room temperature over 1 h. The reaction solution was stirred until the acetophenone disappeared based on TLC. The resulting solution was quenched with 1 mol/l HCl. The usual workup provided (1R)-1-phenylethanol. These results are shown in Table 1. The reaction in THF, ether, or hexane gave (1R)-1-pheny...

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“…The decrease in enantioselectivity for the reduction of the ketone 4-methyloxyacetophenone may be rationalized to the coordination of the heteroatom with the boron atom in the catalyst and borane. [31][32][33] Probably because of steric effects, ketones containing substitution at the ortho position and lacetonaphthone gave lower enantioselectivities ( Table 2, entries 7-9). The ee values of the corresponding product decreased with increasing size of alkyl group (Table 2, entries 1 and 10).…”

Section: Resultsmentioning

confidence: 99%

Synthesis of a new C₂‐symmetric chiral catalyst and its application in the catalytic asymmetric borane reduction of prochiral ketones

Zhou¹,

Wang²,

Dou³

et al. 2007

Chirality

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A new C(2)-symmetric chiral catalyst 3,5-bis[(2S)-(hydroxy-diphenylmethyl)- pyrrolidin-1-ylmethyl]-1,3,4-oxadiazole was successfully synthesized by the reaction of 2,5-dichloromethyl-1,3,4-oxadiazole with (S)-alpha,alpha-diphenyl-2-pyrrolidinemethanol, and applied to the catalytic asymmetric reduction of prochiral ketones with borane. When the catalyst loading was 1 mol %, enantiomeric excesses of up to 86.8% and 94.5% were observed in reduction of aromatic and alpha-halo ketones, respectively.

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A Practical Method for Asymmetric Borane Reduction of Prochiral Ketones Using Chiral Amino Alcohols and Trimethyl Borate

Cited by 88 publications

References 0 publications

Preparation of highly optically pure homochiral sulfide‐containing alcohols via oxazaborolidine‐catalyzed asymmetric borane reduction of ketones

Preparation of highly optically pure homochiral sulfide‐containing alcohols via oxazaborolidine‐catalyzed asymmetric borane reduction of ketones

Asymmetric Borane Reduction of Prochiral Ketone Using Chiral Bis(.ALPHA.,.ALPHA.-diphenyl-2-pyrrolidinemethanol) Carbonate.

Synthesis of a new C₂‐symmetric chiral catalyst and its application in the catalytic asymmetric borane reduction of prochiral ketones

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A Practical Method for Asymmetric Borane Reduction of Prochiral Ketones Using Chiral Amino Alcohols and Trimethyl Borate

Cited by 88 publications

References 0 publications

Preparation of highly optically pure homochiral sulfide‐containing alcohols via oxazaborolidine‐catalyzed asymmetric borane reduction of ketones

Preparation of highly optically pure homochiral sulfide‐containing alcohols via oxazaborolidine‐catalyzed asymmetric borane reduction of ketones

Asymmetric Borane Reduction of Prochiral Ketone Using Chiral Bis(.ALPHA.,.ALPHA.-diphenyl-2-pyrrolidinemethanol) Carbonate.

Synthesis of a new C2‐symmetric chiral catalyst and its application in the catalytic asymmetric borane reduction of prochiral ketones

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Synthesis of a new C₂‐symmetric chiral catalyst and its application in the catalytic asymmetric borane reduction of prochiral ketones