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1.
Catalytic hydrogenation of 1,3-enynes 1a-7a in the presence of ethyl pyruvate and related activated ketones using chirally modified cationic rhodium catalysts results in reductive coupling to afford dienylated alpha-hydroxy esters 1b-7b and 3c-3f with exceptional levels of regio- and enantiocontrol. These studies represent the first highly enantioselective direct catalytic reductive couplings of alkynes to ketones. As illustrated by the conversion of 6b to 6c-6h, the diene containing the side chain of the coupling products is subject to diverse chemo- and regioselective manipulation. Reductive coupling of enyne 6a and ethyl pyruvate using elemental deuterium provides the monodeuterated product deuterio-6b, consistent with a catalytic mechanism involving alkyne-carbonyl oxidative coupling followed by hydrogenolytic cleavage of the resulting oxametallacycle, as corroborated by ESI-MS analysis. 相似文献
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[STRUCTURE: SEE TEXT] Hydrogen-mediated reductive coupling of glyoxal 2 and 1,3-enyne 3 provides alpha-hydroxy ketone 4 in 70% yield and 91% enantiomeric excess. Notably, the benzylic ether and diene side chain of 4 remain intact under the conditions of hydrogen-mediated coupling. In four steps, alpha-hydroxy ketone 4 is converted to pyrans 8 and 9, which embody key structural features of the bryostatin recognition domain. 相似文献
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《Tetrahedron》2014,70(51):9668-9675
The reductive coupling of isatins with ketones and aldehydes by Zn–TiCl4 in THF gave two- and four-electron reduced products, 3-hydoxy-3-(1-hydoxyalkyl)oxindoles and 3-alkylideneoxindoles, selectively by controlling the reaction conditions. Although the 3-(1-hydoxyalkyl)oxindoles were also produced as the four-electron reduced products in some cases, these products were readily dehydrated to 3-alkylideneoxindoles. The 3-alkylideneoxindoles derived from aldehydes were formed as mixtures of geometric isomers. The both geometric isomers were isomerized to the equilibrium mixtures by reflux in cat. PPTS/benzene. 相似文献
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We achieved highly enantioselective synthesis of cyclic 1,2-sulfamidates and -sulfamides via rhodium-catalyzed transfer hydrogenation, and also revealed one-pot preparation of cyclic N-sulfonylimines from α-hydroxy ketones. 相似文献
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Rhodium-catalyzed hydrogenation of 1,3-enynes 1a-8a and 1,3-diynes 9a-13a at ambient temperature and pressure in the presence of ethyl (N-tert-butanesulfinyl)iminoacetate and ethyl (N-2,4,6-triisopropylbenzenesulfinyl)iminoacetates, respectively, results in reductive coupling to afford unsaturated alpha-amino acid esters 1b-13b in good to excellent yields with exceptional levels of regio- and stereocontrol. Further hydrogenation of the diene containing alpha-amino acid esters 1b-8b using Wilkinson's catalyst at ambient temperature and pressure results in regioselective reduction to afford the beta,gamma-unsaturated alpha-amino acid esters 1c-8c in good to excellent yields. Exhaustive hydrogenation of the unsaturated side chains of the Boc- and Fmoc-protected derivatives of enyne and diyne coupling products 14b-16b occurs in excellent yield using Crabtree's catalyst at ambient temperature and pressure providing the alpha-amino acid esters 14d-16d, which possess saturated side chains. Finally, cross-metathesis of the Boc-protected reductive coupling product 14b with cis-1,4-diacetoxy-2-butene proceeds readily to afford the allylic acetate 14e. Isotopic labeling studies that involve reductive coupling of enyne 1a and diyne 9a under an atmosphere of elemental deuterium corroborate a catalytic mechanism in which oxidative coupling of the alkyne and imine residues is followed by hydrogenolytic cleavage of the resulting metallacycle. A stereochemical model accounting for the observed sense of asymmetric induction is provided. These studies represent the first use of imines as electrophilic partners in hydrogen-mediated reductive carbon-carbon bond formation. 相似文献
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[reaction: see text] The rhodium(I)-catalyzed methylenation of functionalized fluorinated ketones using trimethylsilyldiazomethane proceeds to give the corresponding fluoromethylalkenes in good yields (61-90%). Remarkable chemoselectivity was observed for the synthesis of keto-substituted organofluorine alkenes. 相似文献
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Aryl substituted cyclopropyl ketones are cleaved to acyclic ketones with zinc and zinc chloride or with zinc alone in refluxing alcohol. 相似文献
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This reports first intermolecular coupling of unactivated alkenes, including isomerizable alkenes, to a range of heterocycles using a Rh(I) catalyst. A variety of functional groups were incorporated, including esters, nitriles, and acetals. The intermolecular coupling became possible after it was discovered that weak acids dramatically increase the rate of both the inter- and intramolecular reactions. 相似文献
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Bee C Han SB Hassan A Iida H Krische MJ 《Journal of the American Chemical Society》2008,130(9):2746-2747
We report the first enantioselective reductive aldol couplings of vinyl ketones, which were achieved through the design of a novel monodentate TADDOL-like phosphonite ligand. Specifically, hydrogenation of commercially available methyl vinyl ketone (MVK) or ethyl vinyl ketone (EVK) in the presence of aldehydes 1a-7a using cationic rhodium catalysts modified by chiral TADDOL-like phosphonite ligands AP-I and AP-IV produces aldol adducts 1b-7b and 1c-7c with excellent control of relative and absolute stereochemistry. The absolute stereochemical assignments of the aldol adducts are made in analogy to that determined for the 5-bromophthalimido derivative of aldol adduct 1b and the 2-bromo-5-nitrobenzoate of 3b, which were established by single-crystal X-ray diffraction analysis using the anomalous dispersion method. 相似文献
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Ilkka SimpuraVesa Nevalainen 《Tetrahedron》2003,59(38):7535-7546
Bidentate aluminum chelates derived from biphenol, binaphthol and catechol were found to be efficient catalysts for aldol-transfer reactions of ketone to ketone aldol adducts with aliphatic or aromatic aldehydes giving rise to the formation of aldol adducts of ketones to the aldehydes. In the presence of an excess of an aliphatic aldehyde, a catalytic tandem aldol-transfer—Tischtschenko reaction is observed. The tandem reaction produces monoesters of 1,3-diols with high anti selectivity and with modest to good chemical yield. 1,2-Unsaturated aldehydes are less reactive in the aldol-transfer reaction and require 2-4 times higher load of the catalyst to be used than aliphatic and aromatic aldehydes. Poor diastereoselectivity was observed in the formation of α-substituted aldols and 2-substituted monoesters of anti-1,3-diols indicating that the aldol-transfer reaction is not diastereoselective with the catalysts studied. The utility of the highly 1,3-anti selective formation of diolmonoesters was found to be limited by acyl migration. 相似文献
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Stereoselective synthesis of cyclohexanones via phase transfer catalyzed double addition of nucleophiles to divinyl ketones 总被引:1,自引:0,他引:1
Silvanus AC Groombridge BJ Andrews BI Kociok-Köhn G Carbery DR 《The Journal of organic chemistry》2010,75(21):7491-7493
Functionalized cyclohexanones are formed in excellent yield and diastereoselectivity from a phase transfer catalyzed double addition of active methylene pronucleophiles to nonsymmetrical divinyl ketones. 相似文献
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Jang HY Hughes FW Gong H Zhang J Brodbelt JS Krische MJ 《Journal of the American Chemical Society》2005,127(17):6174-6175
Asymmetric hydrogenation of 1,6-enynes using chirally modified cationic rhodium precatalysts enables enantioselective reductive cyclization to afford alkylidene-substituted carbocycles and heterocycles in a completely atom economical fashion. Good to excellent yields and exceptional levels of asymmetric induction are observed across a structurally diverse set of substrates. Mechanistic studies involving hydrogen-deuterium crossover experiments, along with the observance of nonconjugated cycloisomerization products 14c and 15c, suggest rhodium(III) metallocyclopentene formation occurs in advance of hydrogen activation. This oxidative coupling-hydrogenolytic cleavage motif should play a key role in the design of related hydrogen-mediated couplings. 相似文献
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《Tetrahedron: Asymmetry》2001,12(7):1025-1034
Prochiral aryl and dialkyl ketones were enantioselectively reduced to the corresponding alcohols using whole cells of the white-rot fungus Merulius tremellosus ono991 as a biocatalytic reduction system and ruthenium(II)–amino alcohol and iridium(I)–amino sulfide complexes as metal catalysts in asymmetric transfer hydrogenation. Comparison of the results showed that the corresponding chiral alcohols could be obtained with moderate to high enantioselectivities (e.e.s of up to 98%). The biocatalytic and transfer hydrogenation approaches appear to be complementary. The biocatalytic approach is the most suitable for the enantioselective reduction of chloro-substituted (aryl) ketones, whereas in the reduction of α,β-unsaturated compounds excellent results were obtained using the catalytic hydrogenation protocol. 相似文献
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[reaction: see text] A new three-component halo aldol reaction has been discovered for the tandem formations of I-C/C-C bonds by activating the alpha',beta-positions of alpha,beta-acetylenic ketones. The key intermediates, 1-iodo-3-siloxy-1,3-butadienes, were generated from allenolates and directly monitored by (1)H NMR spectroscopic analysis. Excellent geometric selectivity (>95%) and good yields (65-82%) have been achieved for 10 examples. 相似文献
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Katayoun Marjani Maryam Asgari Akram Ashouri Gholam Hossein Mahdavinia Hossien Abbastabar Ahangar 《中国化学快报》2009,20(4):401-403
Under microwave irradiation,the corresponding hydroxycyciopentenones were prepared in high yields by the cross-aldol reactions of benzil with various ketones.When the reactions were performed in vailOUS solvents under classical heating for a long time,they produced the products in relatively low yields. 相似文献
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[reaction: see text] Methyl mandelate undergoes quantitative oxidative homocoupling on treatment with TiCl4/amine at room temperature. In the presence of ArCHO, quantitative syn-diastereoselective aldol condensation takes over the dimerization, whereas exclusive Mannich-type syn-diastereoselective reaction is observed in the presence of both ArCHO and PhNH2. The subsequent reactions of the title intermediate do not depend on how it is generated. 相似文献