- Exhaustive Reduction of Esters Enabled by Nickel Catalysis
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We report a one-step procedure to directly reduce unactivated aryl esters into their corresponding tolyl derivatives. This is achieved by an organosilane-mediated ester hydrosilylation reaction and subsequent Ni/NHC-catalyzed hydrogenolysis. The resulting conditions provide a direct and efficient alternative to multi-step procedures for this transformation that often require the use of hazardous metal hydrides. Applications in the synthesis of -CD3-containing products, derivatization of bioactive molecules, and chemoselective reduction in the presence of other C-O bonds are demonstrated.
- Cook, Adam,Prakash, Sekar,Zheng, Yan-Long,Newman, Stephen G.
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supporting information
p. 8109 - 8115
(2020/05/20)
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- Mild partial deoxygenation of esters catalyzed by an oxazolinylborate-coordinated rhodium silylene
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An electrophilic, coordinatively unsaturated rhodium complex supported by borate-linked oxazoline, oxazoline-coordinated silylene, and N-heterocyclic carbene donors [{κ3-N,Si,C-PhB(OxMe2)(OxMe2SiHPh)ImMes}Rh(H)CO][HB(C6F5)3] (2, OxMe2 = 4,4-dimethyl-2-oxazoline; ImMes = 1-mesitylimidazole) is synthesized from the neutral rhodium silyl {PhB(OxMe2)2ImMes}RhH(SiH2Ph)CO (1) and B(C6F5)3. The unusual oxazoline-coordinated silylene structure in 2 is proposed to form by rearrangement of an unobserved isomeric cationic rhodium silylene species [{PhB(OxMe2)2ImMes}RhH(SiHPh)CO][HB(C6F5)3] generated by H abstraction. Complex 2 catalyzes reductions of organic carbonyl compounds with silanes to give hydrosilylation products or deoxygenation products. The pathway to these reactions is primarily influenced by the degree of substitution of the organosilane. Reactions with primary silanes give deoxygenation of esters to ethers, amides to amines, and ketones and aldehydes to hydrocarbons, whereas tertiary silanes react to give 1,2-hydrosilylation of the carbonyl functionality. In contrast, the strong Lewis acid B(C6F5)3 catalyzes the complete deoxygenation of carbonyl compounds to hydrocarbons with PhSiH3 as the reducing agent.
- Xu, Songchen,Boschen, Jeffery S.,Biswas, Abhranil,Kobayashi, Takeshi,Pruski, Marek,Windus, Theresa L.,Sadow, Aaron D.
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supporting information
p. 15897 - 15904
(2015/09/15)
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- Hydrogenation of substituted aromatic aldehydes: Nucleophilic trapping of the reaction intermediate, application to the efficient synthesis of methylene linked flavanol dimers
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The synthesis of dimeric flavanols is the consequence of the possible trapping of the reaction intermediates generated in the course of the reductive hydrogenation of substituted benzaldehydes. The scope of this reaction is investigated.
- Boyer, Fran?ois-Didier,Ducrot, Paul-Henri
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p. 5177 - 5180
(2007/10/03)
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- Phenyl benzisoxazoles as estrogenic agents
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This invention provides estrogen receptor modulators of formula I, having the structure wherein, R1, R2, and R3 are as defined in the specification, or a pharmaceutically acceptable salt thereof.
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Page/Page column 19
(2010/11/30)
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- Method for orthometalation of a carbocyclic aromatic derivative bearing at least an electron donor group
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The invention concerns a method for orthometalation of a carbocyclic aromatic derivative bearing at least an electron donor group, characterised in that it consists in reacting said carbocyclic aromatic derivative with an efficient amount of at least one alkaline metal in the presence of a compound of formula (I): RX, wherein: R represents a hydrocarbon radical having 1 to 20 carbon atoms which can be a saturated or unsaturated, linear or branched, acyclic aliphatic radical; a saturated or unsaturated, monocyclic or polycyclic cycloaliphatic radical; a saturated or unsaturated, linear or branched aliphatic radical bearing a cyclic substituent; and X represents a bromine or chlorine atom.
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Page column 8
(2010/01/31)
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- Palladium-Catalyzed Cross-Coupling Reactions of Highly Hindered, Electron-Rich Phenol Triflates and Organostannanes
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The palladium-catalyzed cross-coupling reaction of highly hindered, electron-rich phenol triflates and organostannanes (Stille reaction) has been studied in a systematic manner.The following are its salient features: (1) electron-rich phenol triflates require triphenylphosphine to undergo palladium-catalyzed cross-couplings; (2) in general, efficient reactions take place only when larger-than-usual amounts (10-15percent) of palladium are employed.On the reagent side, alkyl- (methyl only), allyl-, vinyl- and alkinylstannanes undergo efficient cross-couplings with the titlesubstrates.However, some limitations to this novel entry to 2-substituted resorcinols exist in regard to both substrates and reagents.Thus, conformationally rigid (hexasubstituted) aryl triflates behave poorly, demethylation being an important side reaction.Moreover, alkyl groups other than methyl cannot be introduced because β elimination occurs more rapidly.The potentially powerful synthesis of hindered biaryls has also been studied briefly.In the present conditions, the reaction appears to be limited by the presence of ortho substituents on the arylstannane moiety.
- Saa, Jose M.,Martorell, Gabriel,Garcia-Raso, Angel
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p. 678 - 685
(2007/10/02)
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- The Alkali Metal Reduction of Trimethoxybenzenes in Hydrocarbon Solvents
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A series of trimethoxybenzenes was subjected to reduction in hydrocarbon solvents. 1,2,3-Trimethoxybenzene (1) and 1,2,4-trimethoxybenzene (2) underwent selective demethoxylation in high yields, whereas the 1,3,5-substituted isomer 3 proved resistant to the reduction conditions.The reactions mechanism involves the fission of a methoxyl radical from an initial radical anion.The accompanying side-reactions, i.e. demethylation and deoxygenation, may be suppressed by the addition of n-butanol as a proton source.
- Dubis, Alina T.,Morzycki, Jacek W.,Poplawski, Janusz
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p. 643 - 650
(2007/10/02)
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- Palladium catalyzed cross-coupling of phenol triflates with organostannanes. A versatile approach for the synthesis of substituted resorcinol dimethyl ethers.
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2,6-Dimethoxy-substituted phenol triflates undergo efficient Pd(0) catalyzed cross coupling with organostannanes, thus providing an easy access to substituted resorcinol dimethyl ethers, a common building block of many aromatic polyketides.
- Martorell, Gabriel,Garcia-Raso, Angel,Saa, Jose M.
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p. 2357 - 2360
(2007/10/02)
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- REGIOSELECTIVE REDUCTIVE ALKYLATION OF 1,2,3-TRIMETHOXYBENZENE
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The 2-methoxyl group of 1,2,3-trimethoxybenzene and its 5-methyl-substituted homologue is removed under electron transfer conditions and replaced with an alkyl group in a one-pot procedure.
- Azzena, Ugo,Cossu, Sergio,Denurra, Teresa,Melloni, Giovanni,Piroddi, Anna Maria
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p. 1689 - 1690
(2007/10/02)
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- Synthesis of 9a-Deoxymitomycin Congeners
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The protected mitosane (23) is prepared in stereospecific manner.The key reactions included in the synthetic scheme are (i) Lewis acid-mediated Claisen-type rearrangement of the penta-2,4-dienyl aryl ether (10) to the penta-2,4-dienylphenol (11), (ii) the regioselective incorporation of the alkoxymethyl group at the 1-position of the pentadienyl side-chain in the protected pentadienylhydroquinone (12), and (iii) the stereospecific copper-catalysed double cyclization of the azido(penta-2,4-dienyl)quinone (15) to the 3H-pyrroloindole-5,8-dione (16) in one step.Subsequent stereospecific introduction of the aziridine ring furnishes the target compound (23).
- Naruta, Yoshinori,Nagai, Naoshi,Maruyama, Kazuhiro
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p. 1143 - 1148
(2007/10/02)
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- Structure-Reactivity Studies and Catalytic Effects in the Photosolvolysis of Methoxy-substituted Benzyl Alcohols
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The photosolvolysis of several methoxy-, dimethoxy-, and hydroxy-substituted benzyl alcohols has been studied in aqueous solution.The primary photochemical event is photodehydroxylation, to give a benzyl cation intermediate, which can be trapped by added external nucleophiles.The reaction is via the singlet excited state, based on observation of fluorescence quenching by hydronium ion in a complementary manner with acid catalysis of reaction observed for several derivatives.Solvent isotope effects on fluorescence efficiency and reaction for (7) and (8) provide additional support of singlet-state reactivity for these compounds.Dimethoxy-substituted alcohols are more reactive than monosubstituted compounds, with quantum yields of methanolysis of up to 0.31 for the most reactive compound, 2,6-dimethoxybenzyl alcohol (8).Using a kinetic argument, the quantum yields of the primary photodehydroxylation process has been estimated to be 1.0 +/- 0.1 for this compound.The results observed for the dimethoxy-substituted derivatives suggest the existence of additivity of substituent effects in these photodehydroxylation reactions.
- Wan, Peter,Chak, Becky
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p. 1751 - 1756
(2007/10/02)
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