Enantioselective Catalytic Borane Reductions of Achiral Ketones: Synthesis and Application of New Rigid Catalysts Prepared from (R)-Phenylglycine and (S)-Phenylalanine

Dauelsberg, Ch.; Martens, Jürgen

doi:10.1080/00397919308018602

Cited by 19 publications

(1 citation statement)

References 40 publications

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“…The most common methods for preparing heterocycles with O-B-N grouping are reactions of 1,2-and 1,3-aminoalcohols with alkyl-and arylboronic acids [10e,13] or dialkyl-and diarylborinic acids [14], boronate [15] or borane [16] and borane-dimethylsulfide [17]. Another method [18] consists in aminoboration of ketene with dialkyl(dimethylamino)boranes or bromodimethylborane and amine, or reactions of substituted vinyloxyboranes with nitriles [19,20].…”

Section: Introductionmentioning

confidence: 99%

Straightforward access to oxazaborines, diazaborinones and triazaborines by reactions of β-enaminoamides with 4-methylbenzenediazonium tetraphenylborate

Svobodová

Bárta

Šimůnek

et al. 2009

Journal of Organometallic Chemistry

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Section: Introductionmentioning

confidence: 99%

Straightforward access to oxazaborines, diazaborinones and triazaborines by reactions of β-enaminoamides with 4-methylbenzenediazonium tetraphenylborate

Svobodová

Bárta

Šimůnek

et al. 2009

Journal of Organometallic Chemistry

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4‐Hydroxyphenylglycine‐Based Oxazaborolidines for Enantioselective Reductions of Ketones

2007

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Amino alcohols 6 featuring the diphenylhydroxymethyl group are prepared from the commercial amino acid (R)-4-hydroxyphenylglycine 3. Oxazaborolidines generated in situ from the amino alcohols 6 and borane-dimethyl sulfide serve as catalysts in enantioselective reductions of acetophenone. The para-substituents of the phenyl ring at the stereogenic carbon atom have a substantial influence on the enantioselectivity. When mediated by the nonaflate 6d, the reduction of ketones 7, 9, 11, and 13 leads to the carbinols 8, 10, 12, and 14 in 90 to 96 % ee.

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New β‐Amino Alcohols as Chiral Ligands for the Catalytic Enantioselective Reduction of Prochiral Ketones and the Nucleophilic Addition of Diethylzinc to Benzaldehyde

Peper

Martens

1996

Chem. Ber.

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New optically active p-amino alcohols, derived from various acyclic and cyclic amino acids with alkyl groups on the carbino1 carbon atom, were used in the enantioselective reduction of prochiral ketones. The attachment of alkyl groups to the nitrogen atom of the catalyst (R)-lb was shown to influence favorably the enantioselectivity of the addition of diethylzinc to benzaldehyde. In both cases the resulting secondary alcohols were obtained in moderate to high optical yields.The enantioselective reduction of carbonyl groups with a variety of ligands, modified by boron and aluminum hydridescl] and the nucleophilic addition of chelated organometallics to carbonyl compounds [2], are two of the most important asymmetric reactions.Recently, much attention was focused on the preparation of catalysts with a p-amino alcohol structural unit. Both functionalities of the p-amino alcohol react with the hydride to give the corresponding 0xazaborolidine[~1. Remarkably, most of the p-amino alcohols employed in the literature bear aromatic groups, especially on the carbinol carbon atom. Therefore, we investigated enantioselective reactions with p-amino alcohols bearing various alkyl groups on the carbinol carbon atom. The p-amino alcohols employed in this paper derive from (R)-phenylglycine [for (R)-la-g], (9-phenylalanine [for (S)-21, (59-homophenylalanine [for (9-31, (9-teut-leucine [for (S)-4b], and (9-indolinecarboxylic acid [for (S)-5b]. Remarkably, the catalyst (S)-4b is a purely aliphatic Acetophenone and a-chloroacetophenone were used as model substrates for the enantioselective catalytic reduction with borane.The reductions of these prochiral ketones with borane were catalyzed by the oxazaborolidines formed in situ from (R)-la-e to (59-5b and gave the secondary alcohols in chemical yields between 65 and 93%. The oxazaborolidines were not isolated.The results of the reduction of the model ketones with the oxazaborolidines generated from the p-amino alcohols (R)-la-e to (S)-5b are summarized in Table 1. The catalysts (R)-la-e afforded alcohols with (S) configuration and the ligands (S)-2 to (S)-Sb gave alcohols with (R) configuration. The reductions of acetophenone were carried out by using 2 or 10 mol-% of the catalysts mentioned above. In all cases the enantioselectivity increased by increasing the amount of the catalyst. The most satisfactory results were obtained with (R)-lb as catalyst for the reduction of aceto- phenone with borane (88% ee with 2 mol-% and 92% ee with 10 mol-% of catalyst). It is noteworthy that the reduction of acetophenone with borane with 2 mol-% of the p-amino alcohol (R)-ld bearing a phenyl group at the stereogenic center afforded the (S) alcohol with 86% ee. The same reaction with 2 mol-% of the benzyl-substituted pamino alcohol (59-2 gave the (R) alcohol with 78% ee.

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Enantioselective Catalytic Borane Reductions of Achiral Ketones: Synthesis and Application of New Rigid Catalysts Prepared from (R)-Phenylglycine and (S)-Phenylalanine

Cited by 19 publications

References 40 publications

Straightforward access to oxazaborines, diazaborinones and triazaborines by reactions of β-enaminoamides with 4-methylbenzenediazonium tetraphenylborate

Straightforward access to oxazaborines, diazaborinones and triazaborines by reactions of β-enaminoamides with 4-methylbenzenediazonium tetraphenylborate

4‐Hydroxyphenylglycine‐Based Oxazaborolidines for Enantioselective Reductions of Ketones

New β‐Amino Alcohols as Chiral Ligands for the Catalytic Enantioselective Reduction of Prochiral Ketones and the Nucleophilic Addition of Diethylzinc to Benzaldehyde

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