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1.
WANG Hui PEI Wei-wei YE Wei-ping 《高等学校化学研究》2005,21(5):536-539
ovel chiral β-amino alcohols containing sulfide or sulfonyl groups were synthesized from (R)-cysteine. Their chiral induction in the asymmetric borane reduction of prochiral ketones was investigated. Optically active secondary alcohols with moderate or high e. e. values were obtained, and the causes of different enantioselectivities between these two sulfur-containing chiral β-amino alcohols were researched. 相似文献
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The enantioselective reduction of prochiral ketones with NaBH4/Me2SO4/(S)-Me-CBS is described. Borane is generated in situ via the reaction of NaBH4 with Me2SO4 in tetrahydrofuran, which is as efficient as the commercial one. Such in situ–generated borane reagent was applied to reduce prochiral ketones in the presence of chiral oxazaborolidine catalyst directly. The corresponding chiral secondary alcohols were obtained with excellent enantiomeric excesses (93–99% ee) and good to excellent yield (80–99%). 相似文献
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Exnantiocontrolled reduction of prochiral ketones with borane in the presence of homochiral amino alcohols 1 - 4 as enantioselective catalysts afforded the chiral corresponding secondary alcohols in moderate to high (55 to 88 %) optical yields. 相似文献
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《Tetrahedron: Asymmetry》2006,17(23):3244-3247
An oxazaborolidine catalyst is readily prepared in situ at 25 °C in THF using (S)-α,α-diphenylpyrrolidinemethanol and borane generated from tetrabutylammonium borohydride/CH3I reagent system. The oxazaborolidine/BH3 reagent system prepared in this way is useful for the reduction of prochiral ketones to the corresponding alcohols with up to 99% ee. 相似文献
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The effect of borane source on enantioselectivity in the enantiopure oxazaborolidine‐catalyzed asymmetric borane reduction of ketones has been investigated by using (S)‐3,1,2‐oxazaborobicyclo[3.3.0]octane and (S)‐7,3,1,2‐thiaxazaborobicyclo[3.3.0]octane as catalysts. The results indicate that the enantioselective order of different borane sources is borane–dimethyl sulfide < borane–N,N‐diethylaniline < borane–THF for the asymmetric reduction of a ketone under the same conditions. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:740–746, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20370 相似文献
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《Tetrahedron: Asymmetry》2000,11(17):3553-3560
Chiral oxazaborolidines generated in situ from 1,2-amino alcohols and amino alcohol derivatives derived from (1R)-(+)-camphor and borane or trimethyl borate were used as catalysts for the enantioselective reduction of prochiral ketones. 相似文献
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A new chiral β-amino alcohol, (s)-2-amino-1, 1-diphenyl-3-(2-naphthyl)-1-propanol and its use as a catalyst in the enantioselective reduction of prochiral ketones with borane were described. 相似文献
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New chiral hydroxyethers 1a-f were prepared for asymmetric protonation of achiral enolates prepared from prochiral ketones. The enantioselectivity of protonation was highly dependent upon the acidity of the chiral alcohols, the highest enantioselectivity (90% ee) being achieved with 3,5-dichloro-substituted beta-hydroxyether 1c. A salt-free enolate generated from trimethylsilyl enol ether 4 provided product of the highest ee. Unlike other reagents, chloro-substituted alcohols provided almost consistent enantioselections throughout the reaction temperatures examined (-25 to -98 degrees C). Protonation of other aromatic ketones showed selectivity similar to that of 2-methyl-1-tetralone. 相似文献
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《Tetrahedron: Asymmetry》2004,15(9):1495-1499
A systematic study was conducted to formulate the optimal reaction parameters for polymer-supported (PS)-oxazaborolidine catalyzed enantioselective ketone reduction. The B-methylated chiral oxazaborolidine prepared in situ from the previously reported polymers by Degni et al. have been used in the enantioselective borane reduction of some substituted aromatic ketones to afford the corresponding optical active secondary alcohol products. While the linear-bound system shows low enantioselectivity, the cross-linked version affords enantioselectivities almost identical to those of the monomeric model (with up to 96% enantiomeric excesses). 相似文献
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The secondary reduction in the direct and oxazaborolidine‐catalyzed asymmetric borane reduction of ketones was investigated by the use of GC/MS tracing titration and control experiments. The results indicate that the secondary reduction affects the enantioselectivity only in noncoordinated solvents at low temperature and not under the usual catalytic reduction conditions because the intermediate alkoxyborane is unstable and quickly converts to borane and dialkoxyborane. The function of an alcohol additive in the asymmetric borane reduction of ketones is to consume excess borane in the reduction system thus inhibiting noncatalytic reduction, which leads to increased enantioselectivity in the catalytic reduction. 相似文献
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Donghui Wei Mingsheng Tang Wenjing Zhang Jing Zhao Ling Sun Chufeng Zhao Homgming Wang 《International journal of quantum chemistry》2011,111(3):596-605
Recently, chiral spiroborate ester [(R)‐2‐((1,3,2‐dioxaborolan‐2‐yloxy)methyl)pyrrolidine] has been experimentally employed as an effective chiral catalyst in the borane‐mediated asymmetric reduction of prochiral ketones to produce the corresponding secondary alcohols. In this article, we have theoretically investigated the mechanism of the reduction using density functional theory. The results reveal that this reaction is accomplished via four steps. Fully geometry optimized reactants, products, transition states, and intermediates were obtained at the B3LYP/6‐31G (d, p) level. The analysis of these results reveals one pathway that is more energetically favorable, and its associated geometries correlate well with the final products of the reaction. The further calculations show that the solvent effect of THF has no great influence on enantioselectivity of this reduction. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
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《Tetrahedron: Asymmetry》2000,11(21):4329-4340
The catalytic asymmetric borane reduction of prochiral ketones was examined in the presence of chiral diazaborolidine catalysts prepared in situ from chiral β-diamines and borane. Chiral secondary alcohols were obtained with modest to high enantiomeric excesses (up to 92% ee) using (S)-2-[(4-trifluoromethyl)anilinomethyl]indoline 2f. 相似文献
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Five novel chiral ferrocenyl amino alcohols were prepared from natural amino acids and used as catalysts in the asymmetric reduction of prochiral ketones with NaBH4/I2 combination.The incorporation of the ferrocenyl moiety into the molecule of the chiral amino alcohols greatly improved their enantioselectivity in the catalysis.The optically active secondary alcohols were obt5ained in moderate to good enantiomeric excesses and high chemical yields. 相似文献
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Asymmetric reduction of various enantiomerically pure ketones was carried out by using oxazaborolidine catalysts with a variety of achiral and chiral ligands. The efficiency of chiral 1,2-amino alcohols as well as the effect of the stereogenic centers in the substrate on the catalytic asymmetric reduction were studied. It was found that the corresponding secondary alcohols were obtained with extremely high stereoselectivities with the proper choice of chiral ligands although a considerably large double asymmetric induction was observed in some cases. 相似文献
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Asymmetric catalytic activity of the chiral spiroborate esters 1 – 9 with a O3BN framework (see Fig. 1) toward borane reduction of prochiral ketones was examined. In the presence of 0.1 equiv. of a chiral spiroborate ester, prochiral ketones were reduced by 0.6 equiv. of borane in THF to give (R)‐secondary alcohols in up to 92% ee and 98% isolated yields (Scheme 1). The stereoselectivity of the reductions depends on the constituents of the chiral spiroborate ester (Table 2) and the structure of the prochiral ketones (Table 1). The configuration of the products is independent of the chirality of the diol‐derived parts of the catalysts. A mechanism for the catalytic behavior of the chiral spiroborate esters (R,S)‐ 2 and (S,S)‐ 2 during the reduction is also suggested. 相似文献
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手性芳基醇是一类重要的合成砌块,广泛存在于许多生物活性分子以及天然产物中,因此,高效高选择性地构建该类化合物是有机化学家们一直关注的研究热点.金属试剂对羰基化合物的不对称加成是构建手性芳基醇的一个简单高效的方法,其中,有机硼试剂由于其方便易得、稳定、低毒、官能团耐受性好等优点而被广泛用于醛、酮的不对称加成反应中.本文综述了过去二十年来过渡金属催化的有机硼试剂对醛、酮的不对称加成反应研究进展,并介绍了一些方法在生物活性手性分子合成中的应用. 相似文献