关键词： .asymmetric synthesis   chiral ligands   asymmetric reactions   central chirality   ligands with planar  

摘要： A series of chiral ligands with planar chirality were synthesized, and have been shown to be highly efficient catalysts in some asymmetric reactions. The role of central and planar chirality in ligands with multi-chirality was also discussed.

关键词： Oxidation   Reagents  

摘要： Reaction of nitrones and acyl halides gives N-acyloxyiminium species, which are more reactive toward soft carbon nucleophiles than nitrones. Addition of chiral enolates to the N-acyloxyiminium species gave N-hydroxy-beta-amino acid derivatives highly diastereoselectively. Reversal of diastereoselectivity was observed between the boron enolates and titanium enolates. Using this method all of the four stereoisomers of alpha-methyl-beta-phenylalanines can be prepared as enantiomerically pure forms.

关键词： Aldehydes   Stereochemistry   Aldol reactions   Stereoselectivity   Substitution reactions  

摘要： A shortening of the reaction path can be realized by using a series of the chiral oxazaborolidinone-promoted aldol reaction with respect to the practical synthesis of the (+)-acutiphycin seco acid derivative 5. The linear strategy is based on the utilization of five aldol reactions with a sequence of silyl nucleophiles, 7, 8, 35, 10, and 11, in the presence of stoichiometric amounts of the promoter, 1 or 2. The construction of the relative configuration between the stereogenic centers is diastereoselectively controlled by the stereochemistry of the promoter used in the enantioselective aldol reaction, which is nearly independent of that of the substrate (promoter control).

关键词： 苯氧丙酸类除草剂   光活性除草剂   中间体   不对称合成  

摘要： D(+)2-(4-羟基-苯氧基)丙酸(简称D(+)HPA)及其衍生物是合成光活性苯氧丙酸类除草剂的重要中间体,工业上多用D(+)HPA及其衍生物与芳环缩合行威霸、禾草克等除草剂.该文通过对D(+)HPA乙酯(简称D(+)HPE)结构的分析,提出了一种不对称合成D(+)HPE的工艺:由L-乳酸出发,用精馏法合法L-乳酸乙酯.后者与对甲苯磺酰氯在有机碱催化下综合得L-对甲苯磺酰乳酸乙酯.最后,用两种方法实现了L-对甲苯磺酰乳酸乙酯和对苯二酚的双分子亲核取代反应(SN)<,2>,以制备D(+)HPE:其一,由L-对甲苯磺酰乳酸乙酯与对苯二酚的钠盐在氮气保护下在碱性溶液中缩合,产率80%以上,光学纯度90%以上;其二,L-对甲苯磺酰乳酸乙酯在四丁基碘化铵、碳酸钠的催化下,直接与对苯二酚反应,产率高于80%,光学纯度大于90%.探讨了各步的反应、催化机理与存在的问题,通过实验提出了解决问题的方法,在此基础上确定了反应的最佳条件,并对各中间产物进行了提纯、纯度的化学分析或仪器分析.最后,对产物的红外光谱、核磁共振谱进行了分析以确认其结构.

关键词： L-[2-C-13]aspartic acid   chiral glycine equivalent   sodium [2-C-13]acetate  

摘要： L-[2-C-13]Aspartic acid was synthesized by using Dellaria's oxazinone labelled with C-13 at the 3-position, prepared from phenyl [2-C-13]bromoacetate and (S)-2-phenylglycinol, as a chiral glycine equivalent. Phenyl [2-C-13]bromoacetate was derived from sodium [2-C-13]acetate. Alkylation of the [3-C-13]oxazinone with ethyl bromoacetate was achieved with high diastereoselectivity. Finally, sequential deprotection and removal of the chiral auxiliary of the alkylated [3-C-13]oxazinone afforded L-[2-C-13]aspartic acid.

关键词： Amides   Alcohols   Organic reactions   Stereoselectivity   Post-translational modification  

摘要： A highly enantioselective method for the synthesis of 4-alkyl substituted 1,2,3,4-tetrahydroisoquinolines is reported. The key step relies on the asymmetric synthesis of alpha-alkylarylacetic acids by alkylation of their corresponding amides employing (S,S)-(+)-pseudoephedrine as chiral inductor. Subsequent Friedel-Crafts acylation, stereocontrolled reductive amination and Pictet-Spengler cyclization affords the title compounds in excellent yields and enantioselectivities.

关键词： Alcohols   Anions   Cyclization   Stereoselectivity   Mixtures  

摘要： One-pot palladium(0)-catalyzed alkylation and S-N, cyclization of 1,4-dichlorobut-2-ene 1 by the anion of or-substituted carbonitriles 2a-d can provide highly functionalized cyclopropanes (E)-4a-d, diastereoselectivity, (de 88-100%). Several attempts to achieve the asymmetric synthesis of the 1-amino-2-ethenylcyclopropanecarbonitriles (E)-9, by means of this new procedure, i.e., using chiral palladium ligands, chiral aminoacetonitriles (-)- and (+)-12 (from 1-hydroxypinanone) or chiral allyl chlorides (4S)-20b-d and (4R)-20e (from (2S) ethyl lactate) have pointed up the reversibility of the palladium-catalyzed cyclization step, responsible for the low enantioselectivity observed (ee less than or equal to 32%) and for the formation of byproducts, i.e., azepine derivatives 8a,b arising from subsequent aza Cope ring expansion. Molecular mechanics calculations using a modified MM2 type force field adapted to the pi-allyl palladium complexes have explained these results. However, when performed under the Mitsunobu reaction conditions (DEAD, PMe3), therefore, in the absence of palladium catalyst, the S-N, cyclization occurred also diastereoselectively (de > 88%) and provided the enantiomerically enriched 1-amino-2-propenylcyclopropanecarbonitrile (E)-22 (ee > 83%) suitable precursor of (1S,2S)-2,3-methanoamino acids.

关键词： Viruses   Anions   Peptides and proteins   Organic compounds   Hydrogenation  

摘要： Demonstrates the asymmetric synthesis of the carbon(3)alpha fragment of 5,6-dihydro-alpha-pyrone nonpeptidic HIV-1 protease inhibitors, or proteolytic enzyme inhibitors. Formation of beta-ketoester via retrosynthetic analysis of the protease inhibitors; Asymmetric hydrogenation pathway; Synthesis of substituted dihydropyrones.

关键词： Sulfides   Oxides   Alcohols   Peptides and proteins   Alkyls  

摘要： The enzyme Coprinus peroxidase (CiP) was employed for the kinetic resolution of racemic hydroperoxides 1 and the asymmetric sulfoxidation of prochiral sulfides 4. Eleven hydroperoxides 1a-k were reduced by CiP and guaiacol as reductant under conditions of kinetic resolution with enantioselectivities of up to >98% for the (S)-hydroperoxide 1 and 90% for the (R)-alcohol 2. In the absence of a reductant, the hydroperoxide la afforded with CiP enantiomerically enriched hydroperoxide 1a (ee up to 54%) and alcohol 2a tee up to 40%), as well as ketone 3a (which is also formed simultaneously in all other reactions) and molecular oxygen. Catalase activity was established for CiP with hydrogen peroxide. When aryl alkyl sulfides 4 were used as oxygen accepters, three products, sulfoxides 5, alcohols 2, and hydroperoxides 1, were obtained, all in enantiomerically enriched form. The highest ee value (89%) was achieved for the sulfoxide derived from naphthyl methyl sulfide (4f). Thus, CiP may be utilized for the asymmetric synthesis of optically active hydroperoxides 1, alcohols 2, and sulfoxides 5.

关键词： Enantioselective synthesis   Diols   Ethers   Metathesis   Aldol reactions  

摘要： A strategy is described for the enantioselective construction of medium-ring cyclic ethers by merging the asymmetric aldol addition of glycolates with a ring-dosing metathesis reaction. Cyclic ethers of seven-, eight-, and nine-membered rings are readily available through a ring-closing metathesis without cyclic conformational constraints, by exploiting the acyclic conformational bias of the gauche effect. A short formal synthesis of the eight-membered ether (+)-laurencin, a red algae metabolite, has been accomplished utilizing the aldol-metathesis combination.