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1.
Two facile accesses to mono-cinchona alkaloid-derived ligands, by conventional heating conditions and solvent-free microwave irradiation, are described. 1,4-Dichlorophthalazine (PHAL) or 3,6-dichloropyridazine (PYDZ) reacted with quinine (QN), cinchonine (CN), or cinchonidine (CND) by using CaH2 as acid-bonding reagent in DMF at 90–100°C to provide mono-cinchona alkaloid-derived ligands 2a–f (87–95%) in 1.5 h. However, the coupling reactions were performed under solvent-free microwave conditions to yield 2a–f (64–89%) within 15 min.  相似文献   

2.
Prior studies have shown an effective way to produce diverse ligand sets for catalyst discovery is by using mixtures of monodentate forms to generate catalysts in situ. Research described here was performed to illustrate that alkene-functionalized monodentate ligands could be used in this way and in another that increases the diversity of the ligand library in an interesting way. Specifically, we hypothesized that as well as being used as monomers, these alkenes could be cross metathesized in situ immediately before the catalysis step. This combination of metathesis to form ligands in situ, then catalysis is referred to here as metacatalysis. In the event, a library of quinidine and quinine alkaloid-derived phosphites were tested as mixtures of monomers and dimers formed via metathesis in situ. The data obtained illustrated that metacatalysis can be used to identify ligands that positively and negatively modulate enantioselectivities in iridium-mediated hydrogenations of α,β-unsaturated carboxylic acid derivatives, relative to the mixtures of the monomeric forms used.  相似文献   

3.
Cinchona alkaloid-derived chiral bifunctional thiourea organocatalysts were synthesized and applied in the Michael addition between nitromethane and chalcones with high ee and chemical yields.  相似文献   

4.
Xiaolei Hu 《Tetrahedron letters》2009,50(30):4378-1707
Enantioselective trifluoromethylation of aromatic ketones promoted by the cinchona alkaloid-derived ammonium bromide and sodium hydride was described. A series of trifluoromethyl-substituted aryl alcohols could be obtained in up to 82% ee with 98% yield under mild conditions. A possible catalytic cycle was also presented.  相似文献   

5.
The catalytic, enantioselective, [4 + 2] cycloaddition reaction of ortho-quinone methides with silyl ketene acetals is described. This mechanistically interesting reaction, initiated by a chiral cinchona alkaloid-derived ammonium fluoride "precatalyst" complex, affords a variety of alkyl- and aryl-substituted 3,4-dihydrocoumarin products in excellent yield and with good enantioselectivity.  相似文献   

6.
2-Amino-8-oxo-tetrahydro-4H-chromene-3-carbonitriles were synthesized for the first time from a tandem Michael addition-cyclization reaction between cyclohexane-1,2-dione and benzylidenemalononitriles. An enantioselective synthesis of these compounds was achieved in moderate ee values (up to 63% ee) by using a cinchona alkaloid-derived thiourea catalyst.  相似文献   

7.
A highly enantioselective Michael addition of malonates to β,γ-unsaturated α-ketoesters was achieved using cinchona alkaloid-derived thioureas as the bifunctional catalyst. The corresponding Michael addition products were obtained in excellent yields (90–99%) and ee values (up to >99% ee) using a quinidine-derived thiourea as the catalyst under neat conditions. The opposite enantiomer may be obtained using a quinine- or cinchonidine-derived thiourea as the catalyst.  相似文献   

8.
The first catalytic enantioselective synthesis of oxaziridines is presented. The oxidation of aryl and alkyl aldimines with m-CPBA under organocatalytic conditions using cinchona alkaloid-derived catalysts furnished optically active oxaziridines in good yields and high enantioselectivities (up to 94% ee). Mechanistic investigations indicate a stepwise enantioselective oxidation process.  相似文献   

9.
《Tetrahedron》2019,75(40):130571
An efficient asymmetric [3 + 2]-cycloaddition reaction of 3-isothiocyanato oxindoles and formaldimines in-situ generated from 1,3,5-trisubstituted-hexahydro-1,3,5-triazines with a cinchona alkaloid-derived thiourea as the catalyst has been developed. A range of biologically important spiro-imidazolidinethione-oxindoles were obtained in excellent yields with good enantioselectivities (up to 99% yield and 93% ee).  相似文献   

10.
《Tetrahedron: Asymmetry》2014,25(8):650-657
The first organocatalytic asymmetric aldol reaction of isocyanoesters with various β,γ-unsaturated α-ketoesters has been described. Using cinchona alkaloid-derived bifunctional thiourea as the catalyst, chiral β-hydroxy-α-amino acid derivatives can be obtained in excellent yields and enantioselectivities (up to 95% yield and 92% ee) after acidic hydrolysis. This protocol provides a straightforward method to access multiple substituted β-hydroxy-α-amino acid derivatives with high enantiomeric purity.  相似文献   

11.
By combining organocatalysis with gold catalysis highly enantioenriched bicyclic enones are available via an operationally simple one-pot procedure. Iminium-ion activation by cinchona alkaloid-derived primary amine catalysts induces the Michael addition of propargylated malononitriles and cyanoacetates to α,β-unsaturated ketones. The resulting intermediates undergo an exo-dig cyclization, forming a new C–C bond followed by double-bond isomerization to give highly functionalized bicyclic enones in good yields and high enantioselectivities.  相似文献   

12.
Guang J  Zhao CG 《Tetrahedron: Asymmetry》2011,22(11):1205-1211
The organocatalytic enantioselective tandem aldol-cyclization reactions of α-isothiocyanato imides and activated carbonyl compounds, such as isatins, an α-ketolactone and a 1,2-dione, have been studied with cinchona alkaloid-derived thiourea-catalysts. This methodology provided an easy way to access enantiomerically enriched spirobicyclic thiocarbamates with high yields and good to excellent stereoselectivity, which have been demonstrated to be useful precursors for the synthesis of biologically active molecules.  相似文献   

13.
《Tetrahedron: Asymmetry》2007,18(4):455-463
The conjugate addition of ethyl α-cyanoacetate with chalcones has been developed. In the presence of cinchona alkaloid-derived thiourea organocatalyst 1i (10 mol %), ethyl α-cyanoacetate could react with various chalcones to afford Michael adducts with high yields (80–92%) and enantioselectivities (83–95% ee).  相似文献   

14.
Direct asymmetric α-benzoyloxylation of α-branched aldehydes and α-branched enals via enamine and dienamine catalysis was used to construct quaternary oxygenated stereocenters with good yields and moderate to good enantioselectivity. This method uses an inexpensive and readily available cinchona alkaloid-derived primary amine as the catalyst, benzoyl peroxide as the oxygen source, and stoichiometric amounts of the aldehyde substrates, providing simple metal-free access to valuable protected 2-hydroxyaldehyde derivatives.  相似文献   

15.
Yoo MS  Jeong BS  Lee JH  Park HG  Jew SS 《Organic letters》2005,7(6):1129-1131
[structure: see text] The Cinchona alkaloid-derived quaternary ammonium salts containing 2'-N-oxypyridine and 2'-cyanobenzene moieties were prepared and evaluated as phase-transfer catalysts in the enantioselective alkylation of glycine imine ester 1. The N-oxypyridine and cyanobenzene moieties might play an important role to form a rigid conformation by coordinating with H(2)O via hydrogen bonding leading to high enantioselectivity (97 approximately >99% ee), which provides evidence of an electronic factor for the high enantioselective catalytic efficiency in phase-transfer alkylation.  相似文献   

16.
An efficient organocatalytic diastereo- and enantioselective Michael addition of α-substituted isocyanoacetates to 2-enoylpyridines catalyzed by cinchona alkaloid-derived squaramide has been achieved, affording the corresponding adducts with two adjacent tertiary-quaternary stereocenters in excellent yields (up to 99%) and good to excellent stereoselectivities (up to >20:1 dr, up to 98% ee) under mild conditions.  相似文献   

17.
A series of cinchona alkaloid-derived dimeric quaternary ammonium salts were prepared as chiral phase-transfer catalysts by the introduction of various functional groups on the phenyl ligand. Among them, the 2-F-substituted derivative 21 showed the highest enantioselectivity in the alkylation of the glycine anion equivalent 1 (97 to >99% ee).  相似文献   

18.
Christiane M. Bode 《Tetrahedron》2006,62(49):11499-11505
Cinchona alkaloid-derived thiourea catalysts promote nucleophilic additions to acyl imines for the asymmetric synthesis of secondary amine adducts. The hydroquinine-derived thiourea catalyst efficiently promotes the aza-Henry reaction of nitroalkane with acyl imines, affording β-nitroamines in good yields with enantioselectivities of 90-98% ee and diastereoselectivities up to 97%. The scope of the reaction also includes dimethyl malonate as a nucleophile to access β-amino esters in high enantiopurity. Under the optimized reaction conditions, secondary amine adducts of high enantiopurity are generated based on various aromatic and α,β-unsaturated acyl imines.  相似文献   

19.
A protocol for the synthesis of isoxazoline N-oxides and its application in the formal synthesis of dehydroclausenamide are described. Sulfonium salt 1 reacts with substituted nitroalkenes smoothly to generate isoxazoline N-oxides in high to excellent yields with dr higher than 99/1. Its asymmetric version has been developed by using cinchona alkaloid-derived ammonium salts 6a and 6b instead of sulfonium salt 1 and higher than 96% ee values are achieved. This method has also been successfully applied to the formal synthesis of dehydroclausenamide.  相似文献   

20.
An efficient stereocontrolled total synthesis of (+)-biotin (1) has been achieved via the intermediacy of Roche's lactone 5 starting from cis-1,3-dibenzyl-2-imidazole-4,5-dicarboxylic acid (2). The bifunctional cinchona alkaloid-derived squaramide-promoted enantioselective alcoholysis was utilizing as a tool for the construction of two contiguous stereocenters of C-3a and C-6a in biotin molecular with excellent enantioselectivity. In addition, the 4-carboxybutyl side chain was assembled by first using C4+C1 approach via a novel tricyclic thiophanium salt intermediate.  相似文献   

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