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Carbon Bond-forming Reactions (carbon + bond-forming_reaction)
Selected AbstractsPhosphotungstic Acid Catalyzed Direct Benzylation of ,-Dicarbonyl CompoundsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 29 2008Guan-Wu Wang Abstract 12-Phosphotungstic acid was used as an efficient, ecofriendly, and air- and moisture-stable catalyst to promote the direct substitution of the hydroxy group of benzylic and allylic alcohols with various ,-dicarbonyl compounds. This powerful protocol for carbon,carbon bond-forming reactions provides monoalkylated dicarbonyl compounds in high yields with great efficiency.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Selective organic synthesis through generation and reactivity control of hyper-coordinate metal speciesTHE CHEMICAL RECORD, Issue 6 2008Tamejiro Hiyama Abstract This paper is a review of my 40 years of research at Kyoto, Sagamihara, and Yokohama, all based on the generation of hyper-coordinate metal species such as ate complexes and pentacoordinate silicates. The topics are: (i) carbenoid reagents for carbon,carbon bond-forming reactions, (ii) nucleophilic substitution at acetal carbons using aluminate reagents, (iii) preparation of magnesium enolates and its reaction with nitriles, (iv) Cr(II) reagents for reduction of organic halides and highly selective carbon,carbon bond formation, (v) organic synthesis with organosilion reagents/fluoride ions, (vi) cross-coupling reaction of organosilicon compounds, and (vii) silicon-based conjugate addition to ,,,-unsaturated carbonyl acceptors. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 337,350; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20162 [source] Ionic Liquids Made with Dimethyl Carbonate: Solvents as well as Boosted Basic Catalysts for the Michael ReactionCHEMISTRY - A EUROPEAN JOURNAL, Issue 45 2009Massimo Fabris Dr. Abstract This article describes 1),a methodology for the green synthesis of a class of methylammonium and methylphosphonium ionic liquids (ILs), 2),how to tune their acid,base properties by anion exchange, 3),complete neat-phase NMR spectroscopic characterisation of these materials and 4),their application as active organocatalysts for base-promoted carbon,carbon bond-forming reactions. Methylation of tertiary amines or phosphines with dimethyl carbonate leads to the formation of the halogen-free methyl-onium methyl carbonate salts, and these can be easily anion-exchanged to yield a range of derivatives with different melting points, solubility, acid,base properties, stability and viscosity. Treatment with water, in particular, yields bicarbonate-exchanged liquid onium salts. These proved strongly basic, enough to efficiently catalyse the Michael reaction; experiments suggest that in these systems the bicarbonate basicity is boosted by two orders of magnitude with respect to inorganic bicarbonate salts. These basic ionic liquids used in catalytic amounts are better even than traditional strong organic bases. The present work also introduces neat NMR spectroscopy of the ionic liquids as a probe for solute,solvent interactions as well as a tool for characterisation. Our studies show that high catalytic efficacy of functional ionic liquids can be achieved by integrating their green synthesis, along with a fine-tuning of their structure. Demonstrating that ionic liquid solvents can be made by a truly green procedure, and that their properties and reactivity can be tailored to the point of bridging the gap between their use as solvents and as catalysts. [source] Bifunctional Heterogeneous Catalysis of Silica,Alumina-Supported Tertiary Amines with Controlled Acid,Base Interactions for Efficient 1,4-Addition ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 41 2009Ken Motokura Dr. Abstract We report the first tunable bifunctional surface of silica,alumina-supported tertiary amines (SA,NEt2) active for catalytic 1,4-addition reactions of nitroalkanes and thiols to electron-deficient alkenes. The 1,4-addition reaction of nitroalkanes to electron-deficient alkenes is one of the most useful carbon,carbon bond-forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA-supported amine (SA,NEt2) catalyst enabled selective formation of a double-alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA,NEt2 catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA,NEt2 catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron-deficient alkenes. The solid-state magic-angle spinning (MAS) NMR spectroscopic analyses, including variable-contact-time 13C cross-polarization (CP)/MAS NMR spectroscopy, revealed that acid,base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid,base interactions. [source] Acid,Base Bifunctional Catalysis of Silica,Alumina-Supported Organic Amines for Carbon,Carbon Bond-Forming ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2008Ken Motokura Dr. Abstract Acid,base bifunctional heterogeneous catalysts were prepared by the reaction of an acidic silica,alumina (SA) surface with silane-coupling reagents possessing amino functional groups. The obtained SA-supported amines (SA,NR2) were characterized by solid-state 13C and 29Si,NMR spectroscopy, FT-IR spectroscopy, and elemental analysis. The solid-state NMR spectra revealed that the amines were immobilized by acid,base interactions at the SA surface. The interactions between the surface acidic sites and the immobilized basic amines were weaker than the interactions between the SA and free amines. The catalytic performances of the SA,NR2 catalysts for various carbon,carbon bond-forming reactions, such as cyano-ethoxycarbonylation, the Michael reaction, and the nitro-aldol reaction, were investigated and compared with those of homogeneous and other heterogeneous catalysts. The SA,NR2 catalysts showed much higher catalytic activities for the carbon,carbon bond-forming reactions than heterogeneous amine catalysts using other supports, such as SiO2 and Al2O3. On the other hand, homogeneous amines hardly promoted these reactions under similar reaction conditions, and the catalytic behavior of SA,NR2 was also different from that of MgO, which was employed as a typical heterogeneous base. An acid,base dual-activation mechanism for the carbon,carbon bond-forming reactions is proposed. [source] Coming of Age: Sustainable Iron-Catalyzed Cross-Coupling ReactionsCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 5 2009Waldemar Maximilian Czaplik Abstract Iron-catalyzed cross-coupling reactions have, over the past years, developed to maturity and today are an integral part of the organic chemist's toolkit. They benefit from low costs, operational simplicity, and high reactivity and thus constitute the "green" sister of the palladium and nickel establishment. This timely Review traces back major achievements, discusses their mechanistic background, and highlights numerous applications to molecular synthesis. Iron-catalyzed carbon,carbon bond-forming reactions have matured to an indispensable class of reactions in organic synthesis. The advent of economically and ecologically attractive iron catalysts in the past years has stepped up the competition with the established palladium and nickel catalyst systems that have dominated the field for more than 30 years, but suffer from high costs, toxicity, and sometimes low reactivity. Iron-catalyzed protocols do not merely benefit from economic advantages but entertain a rich manifold of reactivity patterns and tolerate various functional groups. The past years have witnessed a rapid development with ever-more-efficient protocols for the cross-coupling between alkyl, alkenyl, alkynyl, aryl, and acyl moieties becoming available to organic chemists. This Review intends to shed light onto the versatility that iron-catalyzed cross-coupling reactions offer, summarize major achievements, and clear the way for further use of such superior methodologies in the synthesis of fine chemicals, bioactive molecules, and materials. [source] | ||||||||||