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1.
Reduction intermediate prepared in situ from chiral lactam alcohol 3 and borane at room temperature was found to catalyze the borane reduction of various prochiral ketones with high enantioselectivity up to 98% ee. 相似文献
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[reaction: see text] The Diels-Alder reaction of cyclopentadiene and 2-methacrolein is catalyzed by a chiral Lewis acid to form the exo adduct in 96% yield and 96% ee. 相似文献
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A group of α‐ and β‐N, N‐dialkyl amino ketones were reduced enantioselectively by 2 moles of borane‐tetrahydrofuran in the presence of 10 mol% of the in‐situ formed chiral oxazaborolidine, followed by diluted hydrochloric acid. The resulting amino alcohol‐borane complexes were treated with hydrogen chloride‐glycol‐methanol to give the optically active amino alcohol with the ee up to 99%. 相似文献
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《Tetrahedron: Asymmetry》2014,25(5):457-461
A new prolinamide derivative phthalimido-prolinamide 1 was developed for organocatalytic enantioselective direct aldol reactions of various aldehydes with ketones. The catalytic protocol is effective with 15 mol % of catalyst under solvent free and additive free reaction conditions. By employing a catalytic amount of water, the efficiency of the reaction increased further and the desired products β-hydroxy carbonyl compounds were obtained in high yields and stereoselectivities. 相似文献
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Optically active hydroxyaldehydes arc synthesized in 88–94% e.e. by the catalytic enantioselective addition of dialkylzinc using N,N-dibutylnorephedrine. 相似文献
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Asymmetric Diels-Alder reactions catalyzed by a triflic acid activated chiral oxazaborolidine 总被引:2,自引:0,他引:2
This paper reports a new method for the generation of chiral Lewis superacids by protonation of a non-Lewis acidic oxazaborolidine (1) with triflic acid. The resulting cationic species (3) are powerful and highly enantioselective catalysts for the Diels-Alder reaction of various 1,3-dienes with alpha,beta-enals. An optimization study (see Table 1) led to the selection of reaction conditions and catalysts (6A and 6B) which are very effective. The reactions are simple to conduct, reproducible, and economical, since only ca. 6 mol % of catalyst is required. In addition, the chiral catalyst precursor is readily recovered for reuse (>95% efficiency) and is commercially available. The broad scope of the process is documented by the 14 examples listed in Table 2. The absolute stereochemical course of the Diels-Alder reactions catalyzed by 6A and 6B was successfully predicted on the basis of the mechanistic principles which have recently been formulated for this type of catalytic enantioselective reaction involving re-face attack by the diene on complex 7. The mode of generation of Lewis superacids 6A and 6B allows an approximate comparison (or scale) connecting the catalytic power Lewis and protic acids. 相似文献
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Ding K 《Chemical communications (Cambridge, England)》2008,(8):909-921
This article highlights our recent efforts in the development of highly efficient and cost-effective chiral catalysts for asymmetric reactions through a combinatorial approach by assembling the component ligands (at least one of which is in non-racemic form, while the other might be optically pure, racemic or achiral) with metal ions to generate modular chiral catalyst libraries. The synergistic effect of the binary ligands in terms of both enantioselectivity and activity of the catalysis has been observed in a variety of catalyst systems, including catalysts containing Ti(IV), Zn(II), Rh(I) or Ru(II) ions, for asymmetric hetero-Diels-Alder, carbonyl-ene, alkylation, and hydrogenation reactions, respectively. 相似文献
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Corsifuran A has been prepared in an enantiomerically pure form for the first time by an asymmetric reduction procedure, allowing confirmation of the absolute stereochemistry of the natural product as (R). 相似文献
11.
Ding K Wang Z Wang X Liang Y Wang X 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(20):5188-5197
The development of heterogeneous chiral catalysts for enantioselective reactions is highly desirable in order to overcome some drawbacks of homogeneous catalysts. Different from the conventional approaches by using various types of supports or biphasic systems for the recovery and reuse of homogeneous catalysts, a conceptually new strategy for heterogenization of homogeneous chiral catalysts, that is, a "self-supporting" approach, has been developed to use homochiral metal-organic coordination polymers generated by the self-assembly of chiral multitopic ligands with metal ions, and thus obviates the use of any support. In this concept article, the success of this "self-supporting" strategy will be exemplified in heterogeneous catalysis of asymmetric carbonyl-ene, sulfoxidation, epoxidation, and asymmetric hydrogenation reactions. 相似文献
12.
Velmathi S Balakrishnan U Ananthi N Aldeyab SS Ariga K Naidu TS Vinu A 《Physical chemistry chemical physics : PCCP》2011,13(11):4950-4956
Here we demonstrate for the first time the encapsulation of a chiral oxazaborolidine complex in the 3D mesoporous channels of an amine functionalized KIT-6 material via covalent bonding through a post-synthetic approach. The physico-chemical properties of the pure and immobilized KIT-6 catalysts were obtained by various techniques such as XRD, nitrogen adsorption, HRSEM, UV-Vis diffuse reflectance spectroscopy, and FT-IR spectroscopy. It has been found that the structural stability of the KIT-6 was not affected even after the immobilization of a significant amount of chiral ligand inside the mesoporous channels of the support. However, the values of structural parameters such as the specific surface area and the specific pore volume of the KIT-6 support was significantly lower than the pure KIT-6 support. The chemical interaction between the chiral ligand inside the mesochannels and the KIT-6 support was also confirmed by UV-Vis and FT-IR spectroscopy. The chiral catalytic performance of the immobilized catalysts for the enantioselective reduction of aromatic prochiral ketones was demonstrated and the results were compared with chiral catalyst immobilized supports with uni-dimensional porous structures, such as MCM-41 and SBA-15. Among the catalysts studied, chiral catalyst immobilized KIT-6 showed the highest performance with a high product yield and a high enantioselectivity due to its 3D porous structure with two continuous and interpenetrating systems of chiral channels and an interwoven 3D cylindrical type pores of Ia3d symmetry. The catalyst also exhibited much better recycling capability than other chiral catalyst supported mesoporous materials used in the study. 相似文献
13.
Marchi-Delapierre C Jorge-Robin A Thibon A Ménage S 《Chemical communications (Cambridge, England)》2007,(11):1166-1168
The dinuclear chiral complex Fe(2)O(bisPB)(4)(X)(2)(ClO(4))(4) (X = H(2)O or CH(3)CN) catalyzes with high efficiency (up to 850 TON) and moderate enantioselectivity (63%) the epoxidation of electron deficient alkenes at 0 degrees C by a peracid. 相似文献
14.
Rh2(S-nap)4, a chiral dirhodium tetracarboxamidate complex, has been developed and shown to be an effective catalyst for the asymmetric, intramolecular C-H amination of sulfamate esters. Enantiomeric excesses range from 60-99% for a collection of disparately substituted 3-arylpropylsulfamates. In addition, Rh2(S-nap)4 is found to promote chemoselective allylic C-H oxidation of unsaturated sulfamates, a property not observed with other dirhodium complexes tested to date. 相似文献
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The asymmetric catalytic aldol reaction of silyl allenolates with aldehydes has been achieved by using N-C(3)F(7)CO oxazaborolidine as the catalyst. The fluoroacyl group of the catalyst was found to be crucial for control of enantioselectivity. The reaction provides the first enantioselective approach to beta-halo Baylis-Hillman-type adducts. 相似文献
18.
The strong acid triflimide ((CF3SO2)2NH) protonates chiral oxazaborolidines to form superactive, stable, chiral Lewis acids which are highly effective catalysts for a wide variety of enantioselective Diels-Alder reactions, documented herein by more than 20 examples. 相似文献
19.
The enantioselective Diels-Alder reactions of 1-phenoxycarbonyl-1,2-dihydropyridine with 1-alkylated acryloyl-pyrazolidin-3-ones using chiral cationic palladium-phosphinooxazolidine (Pd-POZ) catalyst afforded chiral isoquinuclidines with excellent enantioselectivity (up to 97% ee). 相似文献
20.
Terada M 《Chemical communications (Cambridge, England)》2008,(35):4097-4112
Binaphthol-derived monophosphoric acids have been designed as novel chiral Br?nsted-acid catalysts. The chiral phosphoric acids thus developed function as efficient enantioselective catalysts for a variety of organic transformations, especially for carbon-carbon bond forming reactions. 相似文献