- Generation of reactive species by one-electron reduction of Fischer-type carbene complexes of group 6 metals and their use for carbon - Carbon bond formation
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Carbon - carbon bond-forming reactions mediated by one-electron reduction of Fischer-type carbene complexes of Group 6 metals were investigated. In the case of aryl- or silylcarbene complexes of tungsten, the anion radical species generated by one-electro
- Fuchibe, Kohei,Iwasawa, Nobuharu
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- Visible-Light-Mediated Reactions of Electrophilic Radicals with Vinyl and Allyl Trifluoroborates
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Visible-light photoredox catalysis enables the vinylation and allylation of electrophilic radicals with readily available potassium trifluoroborate reagents. The processes show good functional group compatibility, and mechanistic and computational studies
- Fernandez Reina, Daniel,Ruffoni, Alessandro,Al-Faiyz, Yasair S. S.,Douglas, James J.,Sheikh, Nadeem S.,Leonori, Daniele
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p. 4126 - 4130
(2017/06/19)
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- Cobalt(i)-catalysed CH-alkylation of terminal olefins, and beyond
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Cobalester, a natural nontoxic vitamin B12 derivative, was found to catalyse unusual olefinic sp2 C-H alkylation with diazo reagents as a carbene source instead of the expected cyclopropanation.
- Giedyk, Maciej,Goliszewska, Katarzyna,ó Proinsias, Keith,Gryko, Dorota
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supporting information
p. 1389 - 1392
(2016/01/25)
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- Chemo- and regioselective reductive transposition of allylic alcohol derivatives via iridium or rhodium catalysis
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We report highly chemo- and regioselective reductive transpositions of methyl carbonates to furnish olefin products with complementary regioselectivity to that of established Pd-catalysis. These Rh- and Ir-catalysed transformations proceed under mild conditions and enable selective deoxygenation in the presence of functional groups that are susceptible to reduction by metal hydrides.
- Lundgren, Rylan J.,Thomas, Bryce N.
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supporting information
p. 958 - 961
(2016/01/20)
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- Ring Expansion of Epoxides under Br?nsted Base Catalysis: Formal [3+2] Cycloaddition of β,γ-Epoxy Esters with Imines Providing 2,4,5-Trisubstituted 1,3-Oxazolidines
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A novel ring-expansion reaction of epoxides under Br?nsted base catalysis was developed. The formal [3+2] cycloaddition reaction of β,γ-epoxy esters with imines proceeds in the presence of triazabicyclodecene (TBD) as a superior Br?nsted base catalyst to afford 2,4,5-trisubstituted 1,3-oxazolidines in a highly diastereoselective manner. This reaction involves the ring opening of the epoxides with the aid of the Br?nsted base catalyst to generate α,β-unsaturated esters having an alkoxide at the allylic position, which would formally serve as a synthetic equivalent of the 1,3-dipole, followed by a cycloaddition reaction with imines in a stepwise fashion. This methodology enables the facile synthesis of enantioenriched 1,3-oxazolidines from easily accessible enantioenriched epoxides.
- Kondoh, Azusa,Odaira, Kenta,Terada, Masahiro
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supporting information
p. 11240 - 11244
(2016/07/06)
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- Borontribromide-mediated C-C bond formation in cyclic ketones: A transition metal free approach
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Borontribromide (BBr3) is a well-known demethylating agent. The current investigation was focused on a new application of borontribromide as a C-C bond forming agent in cyclic ketones. In this study, borontribromide mediated C-C bond formation reactions of tetralones, chromenone, thiochromenone and indanones were explored. A methoxy group containing ketones showed selective C-C bond formation reaction instead of demethylation of the methoxy group. MM2 steric energy calculations for the final products showed that the reaction favored the formation of exo- or endo-cyclic double bond containing products, depending upon their low MM2 steric energy in a specific frame structure, as observed in X-ray crystallography. A comprehensive crystallographic and pi-stacking analysis of product 10a demonstrated the formation of 10a as an enantiomeric mixture, and its centre of inversion was stabilized by a set of three unique pi-pi interactions.
- Ahmad, Imran,Pathak, Vinay,Vasudev, Prema G.,Maurya, Hardesh K.,Gupta, Atul
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p. 24619 - 24634
(2014/07/07)
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- Oxidative alkoxycarbonylation of terminal alkenes with carbazates
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A range of terminal alkenes smoothly underwent palladium-catalyzed oxidative alkoxycarbonylation with carbazates under an oxygen atmosphere to afford structurally diverse α,β-unsaturated esters in moderate to good yields with excellent regioselectivity and E selectivity.
- Su, Yu-Han,Wu, Zhao,Tian, Shi-Kai
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supporting information
p. 6528 - 6530
(2013/07/26)
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- Radical reactions initiated by the photochemical cleavage of carbon-indium bonds of organoindium compounds
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Intra- and intermolecular reactions of carbon-centered radicals generated by photolysis of organoindium compounds were examined. The photolysis of vinylindium compounds and indium acetylides provided vinyl and alkynyl radicals, respectively, which were trapped with ethyl iodoacetate giving the corresponding β,γ-unsaturated esters. Allylic indium compounds, prepared from 8-bromo- or 8-iodooct-1,6-dienes and powdered indium metal, underwent an intramolecular radical cyclization to afford the 5-exo-trig product.
- Hirashita, Tsunehisa,Hayashi, Ayumi,Tsuji, Makoto,Tanaka, Jiro,Araki, Shuki
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p. 2642 - 2650
(2008/09/18)
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- Imidazol(in)ium-2-carboxylates as N-heterocyclic carbene precursors in ruthenium-arene catalysts for olefin metathesis and cyclopropanation
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Five imidazol(in)ium-2-carboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding N-heterocyclic carbenes (NHCs) by reaction with carbon dioxide. They were characterized by IR and NMR spectroscopies, and by TGA. Their ability to act as NHC precursors for in situ catalytic applications was probed in ruthenium-promoted olefin metathesis and cyclopropanation reactions. When visible light induced ring-opening metathesis polymerization of cyclooctene or cyclopropanation of styrene with ethyl diazoacetate were carried out at 60 °C in the presence of [RuCl2(p-cymene)]2, the NHC · CO2 adducts and their NHC · HX counterparts (X = Cl, BF4) displayed similar activities. When metathesis polymerizations were performed at room temperature, the carboxylates proved far superior to the corresponding imidazol(in)ium acid salts. They displayed the same level of activity as the preformed RuCl2(p-cymene)(IMes) complex, whereas the combination of NHC · HX and KO-t-Bu were almost totally inactive. Results obtained for cyclopropanation reactions at room temperature did not show such a large discrepancy of behavior between the two types of adducts.
- Tudose, Adriana,Demonceau, Albert,Delaude, Lionel
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p. 5356 - 5365
(2007/10/03)
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- Radical allylation, vinylation, alkynylation, and phenylation reactions of α-halo carbonyl compounds with organoboron, organogallium, and organoindium reagents
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Allylic gallium and indium reagents are found to mediate radical allylation reactions of α-iodo or α-bromo carbonyl compounds. Treatment of benzyl bromoacetate with allylgallium, prepared from allylmagnesium chloride and gallium trichloride, in the presence of triethylborane provided benzyl 4-pentenoate in excellent yield. Addition of water as a co-solvent improved the yields of allylated products. Allylic indium reagents are also useful and can replace the gallium reagents. A diallylborane reagent can allylate an α-iodo ester in good yield. Alkenylation reactions of α-halo carbonyl compounds with alkenylindium proceeded via a radical process in the presence of triethylborane. Unactivated alkene moieties and styryl groups were introduced by this method. The carbon-carbon double bond geometry of the alkenylindiums was retained during the alkenylation. Preparation of an alkenylindium via a hydroindation of 1-alkyne and subsequent radical alkenylation established an efficient one-pot strategy. Radical alkynylations and phenylations with organoindium reagents are disclosed herein.
- Takami, Kazuaki,Usugi, Shin-Ichi,Yorimitsu, Hideki,Oshima, Koichiro
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p. 824 - 839
(2007/10/03)
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- "Syn-Effect" in the Conversion of (E)-α,β-Unsaturated Esters to the Corresponding β,γ-Unsaturated Esters
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The stereochemistry in the conversion of (E)-α,β-unsaturated esters to the corresponding β,γ-unsaturated esters by treatment with lithium hexamethyldisilazide in the presence of HMPA was investigated. The Z/E ratios of the resulting β,γ-unsaturated esters varied according to the γ-substituents of the (E)-α,β-unsaturated esters. This phenomenon was rationalized by "syn-effect" which may be attributed primarily to σ → π* interaction and/or 6π-electron homoaromaticity.
- Guha, Samar Kumar,Shibayama, Atsushi,Abe, Daisuke,Ukaji, Yutaka,Inomata, Katsuhiko
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p. 778 - 779
(2007/10/03)
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- Reactions of novel reactive species generated by samarium(II)-mediated one-electron reduction of fischer-type carbene complexes
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(matrix presented) Two types of novel reactive species were generated by one-electron reductions of Fischer-type carbene complexes. In the case of tungsten complexes, one-electron reductions generated anion radical species, which added to electron-deficient olefins to give addition products. In the case of chromium complexes, carbonyl insertion occurred to give acyl chromate complexes, which underwent 1,4-addition to various electron-deficient olefins.
- Fuchibe, Kohei,Iwasawa, Nobuharu
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p. 3297 - 3299
(2007/10/03)
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- Ruthenium complexes containing diamine-based ligands as catalysts for insertion of carbenes into O-H bonds of alcohols
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Ruthenium complexes with N-(p-toluenesulfonyl)-diamine ligands are efficient catalysts for insertion of carbenes generated from diazo compounds into O-H bonds of alcohols.
- Simal, Francois,Demonceau, Albert,Noels, Alfred F.
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- Cp*Ru(II) and Cp*Ru(IV)-catalyzed reactions of CHX with vinyl C-H bonds: Competition between double bond homologation and olefin cyclopropanation by alkyl diazoacetate
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When diazoesters are used as carbene precursors, new Ru(II) and Ru(IV) complexes bearing various substitutents tethered ligands mediate the formal carbene insertion into C-H vinyl bonds of (substituted) styrenes to yield mostly E- and Z-styrylacetic esters (e.g. 4-phenylbut-3-enoates with styrene). This rarely observed reaction competes with the cyclopropanation of the double bond. The influence of steric and electronic factors on the two competitive reactions is reported. The observation that the most efficient C-H insertion catalysts also promote the ROMP of norbornene lend support to the formation of ruthenacyclobutanes as reaction intermediates.
- Simal, Francois,Demonceau, Albert,Noels, Alfred F.,Knowles,O'Leary, Shane,Maitlis, Peter M.,Gusev
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p. 163 - 170
(2007/10/03)
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- Cobaloxime-Catalyzed Radical Alkyl-Styryl Cross Couplings
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Cobaloxime-catalyzed radical alkyl-styryl cross couplings can be accomplished by visible light photolysis of various alkyl bromides + styrene + in-situ-generated CoII(dmgH)2py + Zn in refluxing CH3CN or refluxing 95percentEtOH.cobaloximes; radi
- Branchaud, Bruce P.,Detlefsen, William D.
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p. 6273 - 6276
(2007/10/02)
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- Palladium-Catalyzed Decarboxylation-Carbonylation of Allylic Carbonates To Form β,γ-Unsaturated Esters
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Allyl alkyl carbonates undergo a smooth decarboxylation-carbonylation reaction to afford β,γ-unsaturated esters at 50 deg C under atmospheric or low pressure of carbon monoxide and neutral conditions in the presence of palladium-phosphine complexes as catalysts.The reaction offers a very good method for the preparation of β,γ-unsaturated esters from allylic alcohols.
- Tsuji, Jiro,Sato, Koji,Okumoto, Hiroshi
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p. 1341 - 1344
(2007/10/02)
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