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.

Total Synthesis of (-)-Tetrahydrolipstatin by the Tandem Mukaiyama-aldol Lactonization

（-）-Tetrahydrolipstatin 1 was synthesized in three steps and 33.8% overall yield from aldehyde 6 by tandem Mukaiyama-aldol lactonization, which offered a concise, efficient and highly diastereoselective route to this antiobesity drug. We also presented a resolution method for preparation of the crucial intermediate, β- （t-butyldimethylsilyloxy）tetradecanal.

Synthesis of a New β-Mercaptoalcohol

In this letter, (R)-1,1-diphenyl-2-mercapto-3-methyl-1-butanol was synthesized from L-valine and two synthetic routes have been tried.

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.

Reductive amination of ketones with ammonium catalyzed by a newly identified Brevibacterium epidermidis strain for the synthesis of(S)-chiral amines

The asymmetric reductive amination of achiral ketones with ammonia is a particularly attractive reaction for the synthesis of chiral amines.Although several engineered amine dehydrogenases have been developed by protein engineering for the asymmetric reductive amination of ketones,they all display(R)‐stereoselectivity.To date,there is no report of an(S)‐stereoselective biocatalyst for this reaction.Herein,a microorganism named Brevibacterium epidermidis ECU1015 that catalyzes the(S)‐selective reductive amination of ketones with ammonium has been successfully isolated from soil.Using B.epidermidis ECU1015 as the catalyst,the asymmetric reductive amination of a set of phenylacetone derivatives was successfully carried out,yielding the corresponding(S)‐chiral amines with moderate conversion and>99%enantiomeric excess.

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.

Synthesis of Chiral N-Ferrocenylmethylaminoalcohols and their Application in Enantioselective Addition of Diethylzinc to Aldehydes

Three chiral N-ferrocenylmethylaminoalcohols were synthesized from readily available natural L-valine, leucine and phenylanine, and used as chiral ligands in the enantioselective addition of diethylzinc to aldehydes.

Synthesis and Crystal Structure of Chiral 4-Hydroxy-4-butyrolactam Fused Aziridine

A novel compound of chiral 4-hydroxy-4-butyrolactam fused aziridine was synthesized via tandem nucleophilic displacement reaction under mild condition. Its structure was determined by IR, 1H NMR, elemental analysis and X-ray diffraction. The crystal of the new compound is of orthorhombic, space group P212121 with a = 6.4246（6）, b = 13.5081（13）, c = 18.6399（18） A, Mr = 278.39, Z = 4, V = 1617.6（3）A^3, Dc = 1.143 g/cm^3, p（MoKa） = 0.075 mm^-1, F（000） = 608, the final R = 0.0297 and wR = 0.0679.

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.

A Facile Synthesis of the C-11 isomer of 5-epi-Kudtriol

The C-ll isomer of natural trihydroxyl sesquiterpene 5-epi-kudtriol has been synthesized starting from (+)-dihydrocarvone via asymmetric dihydroxylation as a key step.

Studies on Enantioselective Effect of Chiral Titanate Reagents on the Synthesis of Substituted Benzhydrols

Chiral titanate reagents were prepared for inducing asymmetric syntheses of substituted benzhydrols from Grignard reagents and aldehydes. The solvents, reaction temperature and exchange of reactants by crossing experiments were investigated. Favorable attack of the nucleophile upon the aromatic aldehydes' prochiral face was proposed, the absolute configurations of the synthesized benzhydrols were suggested, and a preliminary reaction mechanism was described.

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.