共查询到20条相似文献,搜索用时 15 毫秒
1.
Guofeng Wu 《Tetrahedron letters》2009,50(4):427-3802
Hydrogen transfer reduction of α-sulfonylaldehydes using HCOOH-Et3N system as hydrogen source and (S,S)-TsDPEN-based Ru(II) as catalyst proceeds with dynamic kinetic resolution, providing optically active β-sulfonyl primary alcohols in moderate-to-good yields and up to 90% ee. 相似文献
2.
The dynamic kinetic resolution of β-aryl α-keto esters has been accomplished using a newly designed (arene)RuCl(monosulfonamide) transfer hydrogenation catalyst. This dynamic process generates three contiguous stereocenters with remarkable diastereoselectivity through a reduction/lactonization sequence. The resulting enantioenriched, densely functionalized γ-butyrolactones are of high synthetic utility, as highlighted by several secondary derivatizations. 相似文献
3.
Catalytic dynamic kinetic resolution (DKR) of racemic azlactones with EtOD using squaramide-based dimeric cinchona alkaloid organocatalysts is shown to be a highly effective strategy for the preparation of enantiomerically pure α-deuterated chiral α-amino acids. 相似文献
4.
A kinetic resolution of α-allenic alcohols is realized through chiral silver phosphate-catalyzed cycloisomerization with high stereoselectivity (selectivity factor up to 189) and tolerance of a variety of functional groups. A mechanistic model is proposed to interpret the origin of the high stereoselectivity and broad substrate scope. 相似文献
5.
The asymmetric transfer hydrogenation of β-amido-α-keto esters providing the corresponding anti-β-amido-α-hydroxy esters via dynamic kinetic resolution is reported. The use of a commercially available, or simply prepared, chiral ruthenium catalyst results in good yields as well as high diastereoselectivities and enantioselectivities. 相似文献
6.
Asymmetric nucleophilic substitution reactions of α-bromo α-aryl acetamides derived from l-amino acids are described. The simple and practical syntheses of dipeptide analogues have been developed with dibenzylamine, TBAI and a base to provide 2a-2n and 4 in 50-98% yields with diastereomeric ratios from 74:26 to >99:1. Mechanistic investigations suggest that α-bromo acetamides are configurationally labile under the reaction condition and the primary pathway of the asymmetric induction is a dynamic kinetic resolution. The semiempirical calculations of two epimeric transition states of 1b found that (αS)-epimer is the faster reacting epimer with the formation of an intermolecular hydrogen bond that facilitates delivery of the amine nucleophile. 相似文献
7.
Paola D’Arrigo Lorenzo Cerioli Andrea Fiorati Stefano Servi Fiorenza Viani Davide Tessaro 《Tetrahedron: Asymmetry》2012,23(13):938-944
A double catalyst system (protease + base) was applied to the dynamic kinetic resolution (DKR) of isomeric 1- and 2-α-naphthyl-glycines and -alanines exploiting the in situ racemization of their thioesters. Due to the different C-acidity of the two sets of compounds, different experimental conditions have been devised to perform the simultaneous resolution/racemization process.In all cases, the racemic N-Boc-thioesters were converted into the aminoacids with an l-configuration almost quantitatively and with complete enantioselectivity. 相似文献
8.
Concentration-independent high enantioselectivity in the dynamic kinetic resolution (DKR) of racemic azlactones affording chiral α-aminoesters has been achieved using self-association free thiourea-based dimeric cinchona alkaloid organocatalysts. Detailed experimental studies and single crystal X-ray analysis confirmed that these bifunctional organocatalysts I do not form H-bonded self-aggregates in either solution or solid state. 相似文献
9.
Enantioselective N-acylation of 4-aryl-β-lactams in the presence of acyl transfer catalyst Cl-PIQ provides an effective method for their non-enzymatic kinetic resolution. 相似文献
10.
ZHAO MengMeng LI WanFang MA Xin FAN WeiZheng TAO XiaoMing LI XiaoMing XIE XiaoMin ZHANG ZhaoGuo 《中国科学:化学(英文版)》2013,56(3):342-348
Asymmetric hydrogenation of α-keto Weinreb amides has been realized with [Ru((S)-Sunphos)(benzene)Cl]Cl as the catalyst and CeCl 3·7H2O as the additive.A series of enantiopure α-hydroxy Weinreb amides(up to 97% ee) have been obtained.Catalytic amount of CeCl3·7H2O is essential for the high reactivity and enantioselectivity and the ratio of CeCl3·7H2O to [Ru((S)-Sunphos)(benzene)Cl]Cl plays an important role in the hydrogenation reaction. 相似文献
11.
Zhuqing Liu C.Scott Shultz Candice A. SherwoodShane Krska Peter G. DormerRichard Desmond Claire LeeEdward C. Sherer Joseph ShpunginJames Cuff Feng Xu 《Tetrahedron letters》2011,52(14):1685-1688
An efficient preparation of highly enantiomerically enriched aryl β-hydroxy α-amino esters via dynamic kinetic resolution (DKR), asymmetric transfer hydrogenation of α-amino β-keto esters is described. The anti β-hydroxyl α-amino esters were obtained both in high yields and high diasteroselectivity. The observed high anti selectivity is inconsistent with the previous results in literature. The absolute stereochemistry of the aryl β-hydroxy α-amino esters was unambiguously confirmed via chemical derivatization as well as Vibrational Circular Dichroism (VCD) techniques. 相似文献
12.
Yongtae Kim 《Tetrahedron letters》2007,48(16):2833-2835
Catalytic asymmetric dehydration of β-hydroxy esters via kinetic resolution has been investigated. The kinetic resolution of rac-β-hydroxy esters in the presence of prolinol chiral ligand 2a and BrZnCH2CO2t-Bu can provide highly enantioenriched β-hydroxy esters 3 and 5-11 with selectivity factors ranging from 15 to 42. 相似文献
13.
The first nonenzymatic kinetic resolution of β-lactams has been achieved. Alcoholysis of their N-aroyl derivatives in the presence of a simple chiral acyl transfer catalyst, benzotetramisole, produces β-amino acid derivatives with excellent enantioselectivity. 相似文献
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16.
《Tetrahedron: Asymmetry》1998,9(5):791-796
The lipase-catalyzed kinetic resolutions of the α,β-unsaturated α′-acetoxy ketones 3a,b have been investigated. Of the lipases examined, CAL-B from Candida antarctica (fraction B) has been shown to be an efficient biocatalyst, which may be used effectively in preparative scale reactions. 相似文献
17.
Yosuke Demizu 《Tetrahedron letters》2009,50(37):5241-824
Kinetic resolution of α-hydroxyalkanephosphonates was efficiently performed by benzoylation in the presence of copper(II) triflate and (R,R)-Ph-BOX as a catalyst with excellent s value of up to 286. 相似文献
18.
《Tetrahedron letters》1986,27(47):5759-5762
Chemoselective hydrogenation of various α-nitro ketones was accomplished with 5% Pt sulfide on carbon as a catalyst to afford α-amino ketone hydrochlorides in good yields. 相似文献
19.
《Tetrahedron: Asymmetry》1999,10(5):831-835
Enantiopure β-aminophosphine oxide ligands have been synthesized and used in asymmetric transfer hydrogenation of ketones. Optically active alcohols are obtained in high yields and with up to 84% enantiomeric excess. 相似文献
20.
A new methodology involving the copper(I)-catalyzed enantioselective conjugate reduction of β-boronyl-β-alkyl enoates was developed. Various chiral secondary boronate derivatives can be accessed in excellent yields and good to high levels of enantioselectivity through this efficient copper-catalyzed process using polymethylhydrosiloxane (PMHS) as hydride source. 相似文献