Enantioselective syntheses of various chiral multicyclic compounds with quaternary carbon stereocenters by catalytic intramolecular cycloaddition

The intramolecular cycloaddition of 1,n-diene-ynes (n = 4-6), where alkyne and alkene moieties are connected by a 1,1-disubstituted alkene, was examined using a chiral rhodium catalyst, and various types of cycloadducts with quaternary carbon stereocenter(s) were obtained in high to excellent enantiomeric excess. In the case of 1,4-diene-ynes, tricyclic, bicyclic, and spirocyclic compounds were obtained depending upon the substituents at the 2-position of the 1,4-diene moiety and those at their alkyne termini. On the other hand, 1,5- and 1,6-diene-ynes gave tricyclic and bicyclic compounds, which included medium-sized ring systems. The mechanistic considerations for different reaction pathways and the synthetic transformation of tricyclic products into functionalized spirocyclic compounds are also described. The reaction of enediynes, where two alkyne moieties are connected by a 1,1-disubstituted alkene, was also examined, and sterically strained tricyclic compounds with two carbon stereocenters were obtained.     

Enantioselective acylation of chiral amines catalysed by aminoacylase I

Aminoacylase (E.C. 3.5.1.14) from Aspergillus melleus mediated the acylation of the primary amino group in a range of primary arylalkylamines and amino alcohols in anhydrous organic medium. The commonly used vinyl and isopropenyl esters proved to be unsuitable acyl donors because rapid uncatalysed aminolysis occurred in the presence of these additives. The unwanted aminolysis reaction could be suppressed by performing the enzymatic reaction in tert-butyl methyl ether medium with methyl 2-methoxyacetate as the acyl donor. We found that chiral amines were acylated with poor to moderate enantioselectivity, in contrast with the quantitative enantiodiscrimination that is commonly observed with the corresponding alcohols.     

Enantioselective syntheses of candenatenins B and C using a chiral anthracene auxiliary

The asymmetric syntheses of two anticancer natural products, candenatenins B and C, are described, leading to a revision of the originally assigned stereochemistries. The syntheses follow a Diels-Alder/retro-Diels Alder strategy using a chiral anthracene auxiliary to access both targets with 90% ee. The inherent structural qualities of the auxiliary allow for both regio- and diastereoselective transformations.     

Enantioselective amination of alpha-phenyl-alpha-cyanoacetate catalyzed by chiral amines incorporating the alpha-phenylethyl auxiliary

Nineteen chiral amines and their derivatives were prepared and investigated as organocatalytic Lewis bases in the alpha-amination of ethyl alpha-phenyl-alpha-cyanoacetate. For comparison purposes, a few natural products were also examined as catalysts in this study. Among the results obtained, (R)-N-benzyl-N-(1-phenylethyl)-amine and (R,R)-N,N'-bis(1-phenylethyl)-propane-1,3-diamine as the catalysts afforded the amination products in excellent yields and with up to 84% ee. By contrast, under comparable conditions the two derivatives of natural products (DHQ)2PYR and (DHQD)2PYR provided the product of amination with lower than 10% enantiomeric excess.     

Enantioselective Pd-catalyzed hydrogenation of fluorinated imines: facile access to chiral fluorinated amines

An enantioselective hydrogenation of simple fluorinated imines has been developed using Pd(OCOCF(3))(2)/(R)-Cl-MeO-BIPHEP as a catalyst, and up to 94% ee was achieved. This method provides an efficient route to enantioenriched fluorinated amines.     

Asymmetric synthesis of alpha-branched primary amines on solid support via novel hydrazine resins

[reaction: see text]. Two novel chiral hydrazine resins for asymmetric solid-phase synthesis have been developed. The enantiopure beta-methoxyamino auxiliaries, derived from trans-4-hydroxy-(S)-proline and (R)-leucine, were attached to Merrifield resin and transformed into their corresponding hydrazines. Immobilization of various aldehydes, followed by 1,2-addition of organolithium reagents to the resulting enantiopure hydrazones and reductive cleavage from the solid support, furnished alpha-branched amines, which were isolated as their corresponding amides in good overall yields and enantiomeric excesses of up to 86%.     

New ferrocenyl chiral auxiliary substituents for amines: applications to syntheses of mossambine and vinblastine

(+)-(R)-1,2-(alpha-(R)-Mesyloxy-beta-dimethyltetramethylene)-ferrocene was synthesized and used as a chiral auxiliary for N-alkylation of methyl 1,2,3,4,5,6-hexahydroazepino[4,5-b] indole-5-xi-carboxylates. Condensation with aldehydes then provided tetracyclic products in a diastereomeric ratio of at least 97:3. Gentle cleavage in acetic acid removed the chiral auxiliary to give the corresponding secondary amines in >99% ee. Thus, key intermediates leading to mossambine and vinblastine could be synthesized with high enantioselectivity. The enantioselectivity greatly exceeds that found with other chiral N-auxiliaries developed in our studies.     

Enantioselective syntheses of trans-3,4-difluoropyrrolidines and investigation of their applications in catalytic asymmetric synthesis

[reaction: see text] Asymmetric syntheses of enantiopure trans-3,4-difluoropyrrolidines have been prepared by the introduction of fluorine at both centers in a single operation; asymmetric epoxidations and additions to benzaldehyde were conducted using catalysts whose chirality depends on organofluorine asymmetry.     

Enantioselective separation of racemic secondary amines on a chiral crown ether-based liquid chromatography stationary phase

The first general enantioselective separation of racemic secondary amines on a crown ether-based liquid chromatography chiral stationary phase (CSP) is presented. The CSP is based on (+)- or (-)-(18-crown-6)-2,3,11,12-tetracarboxylic acid covalently bonded to silica gel. A mobile phase containing methanol, acetonitrile, triethylamine and acetic acid was employed in these separations of secondary amines with crown ether CSPs. The separation mechanism is believed to be the secondary amine forming a complex which includes crown ether coordination and electrostatic interaction of the positively charged amine with a carboxylate anion of the immobilized crown ether.     

Enantioselective catalytic ring expansion of methylenecyclopropane carboxamides promoted by a chiral magnesium Lewis acid

A catalytic enantioselective ring expansion of monoactivated methylenecyclopropanes (MCP) in the presence of N-tosyl aldimines was developed using a chiral bis(oxazoline) ligand-MgI2 complex. After evaluation of ligands and optimization of the reaction conditions, the reaction has been applied to a variety of aromatic and heteroaromatic aldimines providing the corresponding trans-C2,C3-disubstituted methylenepyrrolidines in generally good yields (greater than 52%) and up to 86% ee. [reaction: see text].     

手性(salen)Co在不对称催化反应和天然产物合成中 的应用

手性(salen)Co是最近几年发展起来的一种重要的不对称催化剂,受到人们的广泛重视。综述了手性(salen)Co在不对称催化反应和天然产物合成中的一些最新研究进展。     

Enantioselective perception of chiral odorants

This review gives an updated account on the phenomena of enantioselective perception of chiral fragrances employed in fine and functional perfumery, and of some selected flavours. Differences between enantiomers both in odour quality and strength have been considered.     

17.

Enantioselective alkylation of chiral enolates     

D.A. Evans  J.M. Takacs 《Tetrahedron letters》1980,21(44):4233-4236

Alkylations of chiral amide enolates derived from (?)-prolinol have been shown to yield versatile hydroxy-amides in high diastereomeric purity. Their use in the preparation of optically active carboxylic acids is described.     

18.

Enantioselective total syntheses of (+)-decursin and related natural compounds using catalytic asymmetric epoxidation of an enone     

Tetsuhiro NemotoTakashi Ohshima  Masakatsu Shibasaki 《Tetrahedron》2003,59(35):6889-6897

The enantioselective total syntheses of (+)-decursin (1) and related natural dihydropyranocoumarins (−)-prantschimgin (3), (+)-decursinol (4), and (+)-marmesin (5) were achieved for the first time using catalytic asymmetric epoxidation of an enone as the key step. Catalytic asymmetric epoxidation of the enone was effectively promoted by the novel multifunctional asymmetric catalyst generated from La(O-i-Pr)₃, BINOL, and Ph₃AsO in a 1:1:1 ratio to afford epoxide in 94% yield and 96% ee, which was recrystallized to give optically pure epoxide. After conversion to the common key intermediate (−)-peucedanol (7), all natural dihydropyranocoumarins were synthesized through palladium-catalyzed intramolecular C-O coupling reactions. A possible reaction mechanism of the catalytic asymmetric epoxidation of enones is also described based on X-ray analysis, laser desorption/ionization time-of-flight mass spectrometry, kinetic studies, and asymmetric amplification studies.     

19.

Asymmetric syntheses with chiral oxazaborolidines   总被引：2，自引：0，他引：2  

Sabine Wallbaum  Jürgen Martens 《Tetrahedron: Asymmetry》1992,3(12):1475-1504

     

20.

Enantioselective and diastereoselective syntheses of cyanohydrin carbonates     

Yuri N. Belokon'  Ross W. Harrington  Hiroshi Nomura 《Tetrahedron》2007,63(39):9724-9740

A new and general synthesis of alkyl cyanoformates is presented starting from the appropriate alcohol and oxalyl chloride. This is used to prepare enantiomerically pure cyanoformates from enantiomerically pure primary and secondary alcohols. Optimal conditions for the addition of various achiral cyanoformates to aldehydes catalysed by an enantiomerically pure titanium(salen) catalyst in the presence of potassium cyanide as a cocatalyst are developed. Under these conditions, two chiral cyanoformates also reacted with aldehydes to give cyanohydrin carbonates. The stereochemistry of this process is predominantly determined by the stereochemistry of the titanium(salen) catalyst and the stereochemistry of two of the cyanohydrin carbonates was confirmed by X-ray crystallography. In a further extension of the chemistry, a homogeneous system in which the potassium cyanide/18-crown-6 complex is used as the cyanide cocatalyst has been developed and the kinetics of this reaction show that it displays first order kinetics, provided at least 2 mol % of the potassium cyanide complex are employed.     

Enantioselective alkylation of chiral enolates

Alkylations of chiral amide enolates derived from (?)-prolinol have been shown to yield versatile hydroxy-amides in high diastereomeric purity. Their use in the preparation of optically active carboxylic acids is described.     

Enantioselective total syntheses of (+)-decursin and related natural compounds using catalytic asymmetric epoxidation of an enone

The enantioselective total syntheses of (+)-decursin (1) and related natural dihydropyranocoumarins (−)-prantschimgin (3), (+)-decursinol (4), and (+)-marmesin (5) were achieved for the first time using catalytic asymmetric epoxidation of an enone as the key step. Catalytic asymmetric epoxidation of the enone was effectively promoted by the novel multifunctional asymmetric catalyst generated from La(O-i-Pr)₃, BINOL, and Ph₃AsO in a 1:1:1 ratio to afford epoxide in 94% yield and 96% ee, which was recrystallized to give optically pure epoxide. After conversion to the common key intermediate (−)-peucedanol (7), all natural dihydropyranocoumarins were synthesized through palladium-catalyzed intramolecular C-O coupling reactions. A possible reaction mechanism of the catalytic asymmetric epoxidation of enones is also described based on X-ray analysis, laser desorption/ionization time-of-flight mass spectrometry, kinetic studies, and asymmetric amplification studies.     

Enantioselective and diastereoselective syntheses of cyanohydrin carbonates

A new and general synthesis of alkyl cyanoformates is presented starting from the appropriate alcohol and oxalyl chloride. This is used to prepare enantiomerically pure cyanoformates from enantiomerically pure primary and secondary alcohols. Optimal conditions for the addition of various achiral cyanoformates to aldehydes catalysed by an enantiomerically pure titanium(salen) catalyst in the presence of potassium cyanide as a cocatalyst are developed. Under these conditions, two chiral cyanoformates also reacted with aldehydes to give cyanohydrin carbonates. The stereochemistry of this process is predominantly determined by the stereochemistry of the titanium(salen) catalyst and the stereochemistry of two of the cyanohydrin carbonates was confirmed by X-ray crystallography. In a further extension of the chemistry, a homogeneous system in which the potassium cyanide/18-crown-6 complex is used as the cyanide cocatalyst has been developed and the kinetics of this reaction show that it displays first order kinetics, provided at least 2 mol % of the potassium cyanide complex are employed.