Enantioselective synthesis of chiral phosphonylated 2,3-dihydrofurans by copper catalyzed asymmetric formal [3+2] cycloaddition of propargylic esters with β-keto phosphonates

Copper catalyzed asymmetric formal [3＋2] cycloaddition of propargylic esters toβ‐keto phospho‐nates for the synthesis of chiral phosphonylated 2,3‐dihydrofurans was developed. By using a bulky and structurally rigid tridentate ketimine P,N,N ligand, a series of optically active phosphonylated 2,3‐dihydrofurans were prepared in high yield and up to 92%ee.

New Asymmetric Synthesis of Alkannin and Shikonin

A new approach for asymmetric synthesis of alkannin and shikonin is presented. The chiral centers of the targets were introduced via an asymmetric C-arylation of protected chiral glyceraldehyde in high de. The two enantiomers were prepared with the D-isopropylidenegly- ceraldehyde as the starting material.

Asymmetric Synthesis of (-)-1-Trimethylsilyl-ethanol with Immobilized Saccharomyces Cerevisiae Cells in Water/Organic Solvent Diphasic System

Asymmetric synthesis of (-)-1-trimethylsilyl-ethanol with immobilized Saccharomyces cerevisiae cells in water/organic solvent biphasic system was studied. The effects of shake speed, hydrophobicity of organic solvent, volume ratio of water phase to organic phase, pH value of aqueous phase and reaction temperature on the initial reaction rate, maximum yield and enantiomeric excess (ee) of the product were systematically explored. All the above-mentioned factors had significant influence on the reaction. n-Hexane was found to be the best organic solvent for the reaction. The optimum shake speed, volume ratio of water phase to organic phase, pH value and reaction temperature were 150 r.min-1, 1/2, 8 and 30 ℃ respectively, under which the maximum yield and enantiomeric excess of the product were as high as 96.8% and 95.7%, which are 15% and 16% higher than those of the corresponding reaction performed in aqueous phase. To our best knowledge, this is the most satisfactory result obtained.

Asymmetric Pictet-Spengler Reactions:Synthesis of Tetrahydroisoquinoline Derivatives from L-DOPA

The cis-l-substituted-6,7-dihydroxy-l,2,3,4-tetrahydroisoquinoline-3-carboxylic acid esters 3 can be obtained in a highly diastereoselective fashion through 1,3-induction Pictet- Spengler (P-S) cyclization of the L-DOPA (3,4-dihydroxyphenylalanine) methyl ester with aromatic or aliphatic aldehydes under acidic conditions. Their epimers 4 are also obtained as minor products.

Asymmetric Synthesis and Crystal Structure of a Bioactive Morpholine Derivative

A novel morpholine derivative was synthesized by Michael addition/internal nucleophilic substitution of 4-（L）-menthyloxy（1R,2S,5R）-butenolide with phenyl-glyalcohol under mild condition, and its structure was determined by X-ray diffraction. The target compound belongs to orthorhombic, space group P212121 with a = 5.7729（7）, b = 11.5032（14）, c = 25.161（3）A, Mr = 319.35, Z = 4, V = 1670.8（4）A^3, Dc = 1.270 g/cm3, μ（MoKα） = 0.094 mm^-1, F（000） = 680, Flack = 0.01（2）, R = 0.0398 and wR = 0.0914.

Asymmetric Synthesis of α-Substituted-γ-butyrolactone Empolying Prolinol Type of Auxiliaries

Eleven (S)-(-)-bishydrocarbyl-(1-alkanoylpyrrolidin-2-yl)-methanol derivatives of three types were synthesized from L-proline, asymmtrically selective alkylation products were obtained by LDA treatment and alkylation using methyl 2-bromoethyl ether, and three types of chiral α-substituted-γ-butyrolactones were obtained by hydrolyzing the alkylation products, with %e.e. being up to 89 percent.

A CONVENIENT ASYMMETRIC SYNTHESIS OF 1-AMINOALKYLPHOSPHONIC ACIDS^+

A convenient method for the asymmetric synthesis of 1-amino- alkylphosphonic acids was described.It involved the diastereoselctive alkylation of bicyclic chloromethylphosphonamide derived from(S)-2-ani- linomethylpyrrolidine followed by subsequent conversions leading to amino compounds by Staudinger method.Acid hydrolysis afforded the target molecule in good yield.

NATURAL PRODUCTS SYNTHESIS BY RETRO-DIELS-ALDER REACTION Ⅱ~1 ASYMMETRIC SYNTHESIS OF (+) AND (-) 5-OXO-ENDO-TRICYCLO [5.2.1.0.^(2, 6)] DECA-3, 8-DIENE 1 BY ENZYME-CATALYZED REACTION

Asymmetric syntheses of both enantiomerically pure (+) and (-) 5-oxo-endo-tricyclo [5.2.1.0.^(2,6)] deca-3, 8-diene 1 was described. The key step is the use of enzyme-catalyzed hydrolysis of meso-diacetate 5.

Asymmetric synthesis of 3-butylphthalide using isomannide and isosorbide as chiral auxiliaries

A new approach for asymmetric syntheses of （S） and （R）-3-n-butylphthalide （NBP） is presented. The diastereoselective addition of dibutylzinic to aromatic aldehyde 10 or 11 generated from isomannide- or isosorbide-derived chiral auxiliary afforded S-NBP or R-NBP in high optical yields.

ASYMMETRIC SYNTHESIS Ⅻ:HIGHLY ENANTIOSELECTIVE SYNTHESIS OF α-AMINO ACIDS BY ALKYLATION OF THE KETIMINE FROM 2-HYDROXY-PINAN-3-ONE AND MENTHYL GLYCIN-ATE A DOUBLE ASYMMETRIC INDUCTION SYSTEM

A series of α-amino acids are obtained in 72-96% optical yields by alkylation of the ketimine derived from(+)-2-hydroxy-pinan-3-one and(-)-menthyl glycinate fol- lowed by hydrolysis of the alkylated intermediates with mineral acid.The double asymmetric induction are explained by the transition model of lithium enolate.

ASYMMETRIC SYNTHESIS WITH ORGANO-TITANATE REAGENTS COORDINATED BY TARTARATE-LIKE LIGAND

A series of substituted chiral benzhydrols were synthesized by the reaction of aromatic aldehydes with chiral intermediates formed from chiral titanates and arylmagnesium halides.

Asymmetric Synthesis of (-)-(4R, 5R)-4-[5-(Benzo[1, 3]dioxol-5-yl)-4- hydroxyl-1-(pyridin-2-yl)-4, 5-dihydro-1H-pyrazol-3-yl]benzamide

The asymmetric synthesis of （-）-（4R, 5R）-4-[5-（benzo[1, 3]dioxol-5-yl）-4-hydroxyl-1- （pyridin-2-yl）-4,5-dihydro-lH-pyrazol-3-yl]-benzamide with improved Juliá-Colonna asymmetric epoxidation procedure as key step was described.

Asymmetric Synthesis of (R)-and (S)-Moprolol

A simple and effective procedure for the enantioselective synthesis of （R）- and （S）-moprolol was described. The key step was the asymmetric synthesis of enantiopure （R）- and （S）-guaifenesin, which were synthesized from enantioenriched （R）-3-chloro-l,2-propanediol and （S）-epichlorohydrin via kinetics of hydrolysis resolution of racemic epichlorohydrin by chiral Salen-Co^Ⅲ complex. The e.e. values of both the optical compounds were above 98%, and the chemical structures of the target compounds were confirmed by ^1H NMR, ^13C NMR, IR, and MS.

THE ASYMMETRIC SYNTHESIS OF AMINO ACIDS UNDER POLYMER-SUPPORTED PHASE TRANSFER CATALYTIC CONDITION

The optical alpha-amino acids were synthesized under room temperature by alkylation of N-(diphenyl methylene) glycine t-butyl ester under polymer-supported phase transfer conditions using polymer-supported cinchonine (or quinine) alkaloids as chiral phase transfer catalysts and dichloromethane as solvent, followed by hydrolysis of the above intermediates introduced to the final products-optical alpha-amino acids. This is a new method for the asymmetric synthesis of alpha-amino acids. The influences of catalyst, temperature, substrates, and organic solvents on the chemical yield and optical purities of products were studied.

Asymmetric Synthesis of Polyhydroxy Pyrrolidinonyl Nucleoside Analogues from Tartaric acid

Asymmetric synthesis of novel optically active nucleoside analogues 7 from natural tartaric acid is described. In the given nucleoside analogues an optically active polyhydroxy pyrrolidinonyl ring is in place of the tetrahydrofuran ring.

A New Asymmetric Synthesis of (+)-(3R, 4S, 5R, 7S)-Neoclausenamide via Intramolecular Nucleophilic Attack of Carbon Anion onto Cyclic Sulfate

An intramolecular nucleophilic substitution of carbon anion to cyclic sulfate was first employed in asymmetric synthesis of (+)-(3R, 4S, 5R, 7S)-neoclausenamide 1 which is a novel hepatoprotective lactam isolated from the dry leaves of Chinese folk medicine Clausena lansium (Lour) Skeel. The regioselectivity of beta-attack to this cyclic sulfate, just like its epoxide counterpart was attributed to the increased reactivity of beta-position by the phenyl group.

SYNTHESIS OF ASYMMETRIC ETHERS CLEAVAGE OF ACYCLIC ACETALS WITH ZrCl_4-LiAlH_4

In this paper, we investigated the selective cleavage of acyclic acetals with the reagent system, ZrCl_4-LiAlH_4. The results indicate that this system is very useful for the cleavage of acyclic acetals to the corresponding asymmetric ethers.

THE SYNTHESIS AND CHARACTERIZATION OF ASYMMETRIC TRIPYRRANE-CONTAINING MACROCYCLES

An improved procedure was used to prepare the asymmetric tripyrrane-containing macrocycles, The yield was over 85% These maerocycles could be oxidized to the methine bridled 23 (?)-electron aromatic cadmium(Ⅱ)complexes by reating with cadmium chloride in the presence of air and their atructures were characterized.

Asymmetric synthesis of 3β-acetoxy-17,17-ethylendioxy-15β,16β-methylene-5-androsten-7β-ol

acetoxy-17,17-ethylendioxy-15β,16β-methylene-5-androsten-7β-ol（Ⅰ） was prepared by 3 steps from 3β-acetoxy-15β,16β-methylene-5-androsten-17-one （Ⅱ） with overall yield of 52.7%. Thus, interaction of ethylene glycol and material （Ⅱ） gave 3β-acetoxy- 17,17-ethylendioxy-15β,16β-methylene-5-androsten （Ⅲ） which was subsequently oxidated and stereoselectively reduced to produce compound（Ⅰ）. The normal influencing factors, such as the types of oxidants and reductives, the mole ratio of reactants, the reaction temperature, and the addition ways of reactants, in oxidation and reduction were discussed. The results show that the oxidation rate order is CrO3-C5H5N （1∶1, mole fraction）>CrO3-C5H5N（1∶2）>（C5H5NH）2Cr2O7 in terms of the oxidant, the yield of the oxidation becomes higher with increasing the oxidant stoichiometry and raising the reaction temperature. And the optimum condition is that the reaction temperature is at 30 ℃, and n （Ⅲ）/ n （CrO3-C5H5N（1∶2））=1∶20. The yield of the -7β alcohol order with Li[Al（OC（CH3）3）3H] （e.g.78.6%） is more than that with NaBH4 （e.g.14.5%） in terms of the reductive （agent） and the reduction rate decreases in the course of reaction. The compound （Ⅰ） is characterized by IR and MS.