- Zn- And Cu-catalyzed coupling of tertiary alkyl bromides and oxalates to forge challenging C?O, C?S, and C?N bonds
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We describe here the facile construction of sterically hindered tertiary alkyl ethers and thioethers via the Zn(OTf)2catalyzed coupling of alcohols/phenols with unactivated tertiary alkyl bromides and the Cu(OTf)2-catalyzed thiolation of unactivated tertiary alkyl oxalates with thiols. The present protocol represents one of the most effective unactivated tertiary C(sp3)? heteroatom bond-forming conditions via readily accessible Lewis acid catalysis that is surprisingly less developed.
- Gong, Yuxin,Zhu, Zhaodong,Qian, Qun,Tong, Weiqi,Gong, Hegui
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supporting information
p. 1005 - 1010
(2021/02/01)
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- Scalable electrochemical reduction of sulfoxides to sulfides
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A scalable reduction of sulfoxides to sulfides in a sustainable way remains an unmet challenge. This report discloses an electrochemical reduction of sulfoxides on a large scale (>10 g) under mild reaction conditions. Sulfoxides are activated using a substoichiometric amount of the Lewis acid AlCl3, which could be regeneratedviaa combination of inexpensive aluminum anode with chloride anion. This deoxygenation process features a broad substrate scope, including acid-labile substrates and drug molecules.
- Kong, Zhenshuo,Pan, Chao,Li, Ming,Wen, Lirong,Guo, Weisi
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supporting information
p. 2773 - 2777
(2021/04/21)
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- Ni(II) Precatalysts Enable Thioetherification of (Hetero)Aryl Halides and Tosylates and Tandem C?S/C?N Couplings
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Ni-catalyzed C?S cross-coupling reactions have received less attention compared with other C-heteroatom couplings. Most reported examples comprise the thioetherification of most reactive aryl iodides with aromatic thiols. The use of C?O electrophiles in this context is almost uncharted. Here, we describe that preformed Ni(II) precatalysts of the type NiCl(allyl)(PMe2Ar’) (Ar’=terphenyl group) efficiently couple a wide range of (hetero)aryl halides, including challenging aryl chlorides, with a variety of aromatic and aliphatic thiols. Aryl and alkenyl tosylates are also well tolerated, demonstrating, for the first time, to be competent electrophilic partners in Ni-catalyzed C?S bond formation. The chemoselective functionalization of the C?I bond in the presence of a C?Cl bond allows for designing site-selective tandem C?S/C?N couplings. The formation of the two C-heteroatom bonds takes place in a single operation and represents a rare example of dual electrophile/nucleophile chemoselective process.
- Martín, M. Trinidad,Marín, Mario,Maya, Celia,Prieto, Auxiliadora,Nicasio, M. Carmen
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supporting information
p. 12320 - 12326
(2021/08/09)
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- Deprotonated Salicylaldehyde as Visible Light Photocatalyst
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Salicylaldehyde is established as an efficient visible light photocatalyst for the first time. Compared to other simple aldehyde analogies, salicylaldehyde has a unique deprotonative red-shift from 324 to 417 nm and gives rise to the remarkable increase of fluorescence quantum from 0.0368 to 0.4632, thus enabling salicylaldehyde as a visible light (>400 nm) photocatalyst. The experimental investigations suggest that the reactive radical species are generated by sensitization of the substrates by the deprotonated salicylaldehyde through an energy-transfer pathway. Consequently, the C-C cleaving alkylation reactions of N-hydroxyphthalimide esters proceed smoothly in the presence of as low as 1 mol % of salicylaldehyde under the visible-light irradiation, affording desired alkylation products with up to 99% yields. Application in visible-light induced aerobic oxidation of N-alkylpyridinium salts is also reported.
- Zhuang, Yan-Jun,Qu, Jian-Ping,Kang, Yan-Biao
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p. 4386 - 4397
(2020/03/05)
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- Transalkylation of alkyl aryl sulfides with alkylating agents
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The reaction of methyl iodide with tert-butylphenylsulfide in DMF leads to a transalkylation that produces methylphenylsulfide. This transalkylation reaction was further studied by 1H NMR spectroscopy. The polarity of the solvent, the electron density on the sulfur atom, and the strength of the alkylating agent (MeI, EtI, BuI, dimethyl sulfate, or dimethyl carbonate) played important roles in the reaction. The suggested mechanism of the reaction involves the formation of a dialkyl aryl sulfonium salt that subsequently eliminates the radical. This mechanism was supported by the observation of higher conversion rates for compounds with more branched alkyl groups on the sulfur atom, which may lead to the formation of more stable radicals.
- Nawrot, Daria,Koleni?, Marek,Kune?, Ji?í,Kostelansky, Filip,Miletin, Miroslav,Novakova, Veronika,Zimcik, Petr
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p. 594 - 599
(2018/01/01)
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- C-S cross-coupling of aryl halides with alkyl thiols catalyzed by in-situ generated nickel(II) N-heterocyclic carbene complexes
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The C-S cross-coupling of aryl halides with alkyl thiols catalyzed by in-situ generated Ni (II) N-heterocyclic carbene (NHC) complexes is investigated. Good to excellent yields can be obtained for a variety of aryl halides when using 5 mol% of the Ni (II)-NHC catalyst and 1.5 eq. of KOtBu. Both the electronic and steric effects of the NHC ligands on the catalytic performance of Ni (II)-NHC, as well as the electronic effects of aryl halides on coupling reactivity are examined. The mechanism for Ni (II)-NHC catalyzed coupling reactions is also discussed.
- Guo, Fang-Jie,Sun, Jing,Xu, Zhao-Qing,Kühn, Fritz E.,Zang, Shu-Liang,Zhou, Ming-Dong
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- Efficient dehydrative alkylation of thiols with alcohols catalyzed by alkyl halides
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Alcohols can be efficiently converted into the useful thioethers by a transition metal- and base-free dehydrative S-alkylation reaction with thiols or disulfides by employing alkyl halides as the effective catalyst. This simple and efficient method is a green and practical way for the preparation of thioethers, as it tolerates a wide range of substrates such as aryl and alkyl thiols, as well as benzylic, allylic, secondary, tertiary, and even the less reactive aliphatic alcohols.
- Yang, Yaqi,Ye, Zihang,Zhang, Xu,Zhou, Yipeng,Ma, Xiantao,Cao, Hongen,Li, Huan,Yu, Lei,Xu, Qing
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supporting information
p. 9638 - 9642
(2017/11/30)
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- Tert-Butyl Sulfoxides: Key Precursors for Palladium-Catalyzed Arylation of Sulfenate Salts
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The present report describes an efficient and clean generation of sulfenate salts (R1SO-) by pyrolysis of readily available tert-butyl sulfoxides to give sulfenic acids (R1SOH) and traceless isobutene, followed by hydrogen abstraction with a weak inorganic base (K3PO4). The relevance of this process was exemplified through an in situ palladium-catalyzed cross-coupling reaction with aryl halides/triflates leading to aryl sulfoxides. The operationally simple C-S bond-forming protocol developed uses Pd(dba)2 as catalyst and Xantphos as ligand in toluene or a toluene/H2O mixture. Further extensions include the use of di-tert-butyl sulfoxide as an equivalent for sulfur monoxide dianion (SO2-) and the development of diastereoselective versions in the [2.2]paracyclophane and biaryl series.
- Gelat, Fabien,Lohier, Jean-Fran?ois,Gaumont, Annie-Claude,Perrio, Stéphane
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supporting information
p. 2011 - 2016
(2015/06/23)
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- Catalytic C - S cross-coupling reactions employing Ni complexes of pyrrole-based pincer ligands
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A series of catalytic C - S coupling reactions utilizing well-defined Ni(II) PNP pincer complexes as precatalysts are reported (PNP = anion of 2,5-bis[(dialkyl/aryl-phosphino)methyl]pyrrole, abbreviated as P2RPyr). Coupling reactions employing a variety of aryl iodides and thiols in the presence of base and DMF proceed in good to excellent yield at 80°C with low catalyst loadings. Aryl bromides were found to result in substantially lower yields, and aryl chlorides were found to be unreactive under the catalytic conditions. In an effort to further understand the reactivity of the nickel PNP precatalysts, complexes of Ni(II) containing amide, alkoxide, hydroxide, thiolate, and hydrosulfide ligands have been prepared and examined in stoichiometric reactions relevant to carbon-heteroatom coupling. Full characterization of each nickel complex is provided, including solid-state structures. The results of stoichiometric reactions implicate a reduced Ni(I) species as the active catalyst, which forms by reduction of the Ni(II) precatalyst in the presence of excess thiolate. The facility in forming Ni(I) species is invoked to rationalize the observed activity among different Ni PNP precatalysts. (Chemical Equation Presented).
- Venkanna, Gopaladasu T.,Arman, Hadi D.,Tonzetich, Zachary J.
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p. 2941 - 2950
(2015/02/19)
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- Structural effects on the C-S bond cleavage in aryl tert -butyl sulfoxide radical cations
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The oxidation of a series of aryl tert-butyl sulfoxides (4-X-C 6H4SOC(CH3)3: 1, X = OCH 3; 2, X = CH3; 3, X = H; 4, X = Br) photosensitized by 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ+) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Products deriving from the C-S bond cleavage in the radical cations 1+?-4+? have been observed in the steady-state photolysis experiments. By laser irradiation, the formation of 3-CN-NMQ? (λmax = 390 nm) and 1 +?-4+? (λmax = 500-620 nm) was observed. A first-order decay of the sulfoxide radical cations, attributable to C-S bond cleavage, was observed with fragmentation rate constants (k f) that decrease by increasing the electron donating power of the arylsulfinyl substituent from 1.8 × 106 s-1 (4 +?) to 2.3 × 105 s-1 (1 +?). DFT calculations showed that a significant fraction of the charge is delocalized in the tert-butyl group of the radical cations, thus explaining the small substituent effect on the C-S bond cleavage rate constants. Via application of the Marcus equation to the kinetic data, a very large value for the reorganization energy (λ = 62 kcal mol-1) has been calculated for the C-S bond scission reaction in 1+?-4 +?.
- Cavattoni, Tullio,Del Giacco, Tiziana,Lanzalunga, Osvaldo,Mazzonna, Marco,Mencarelli, Paolo
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p. 4886 - 4894
(2013/07/11)
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- Synthesis of sulfides under solvent- and catalyst-free conditions
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A simple, highly efficient, and green protocol has been developed for preparation of sulfides from alkyl or aryl thiols and benzyl-, allyl-, t-butyl, and adamantyl halides under solvent- and catalyst-free conditions.
- Movassagh, Barahman,Soleiman-Beigi, Mohammad
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experimental part
p. 409 - 411
(2010/05/01)
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- Resting state and elementary steps of the coupling of aryl halides with thiols catalyzed by alkylbisphosphine complexes of palladium
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Detailed mechanistic studies on the coupling of aryl halides with thiolscatalyzed by palladium complexes of the alkylbisphosphine ligand CyPF- t Bu (1-dicyclohexylphosphino-2-di-tert-butylphosphinoethylfer rocene) are reported. The elementary steps that constitute the catalyticcycle, i.e. oxidative addition, transmetalation and reductive eliminati on, have been studied, and their relative rates are reported. Each of the steps of the catalytic process occurs at temperatures that are much lower than those required for the reactions catalyzed by a combination of palladium precursors and CyPF- t Bu. To explain these differences in rates between the catalytic and stoichiometric reactions, studies were conducted to identify the resting state of the catalyst of the reactions catalyzed by a combination of Pd(OAc)2 and CyPF- t Bu, a combination of Pd(dba) 2 and CyPF- t Bu, or the likely intermediate Pd(CyPF- t Bu)(Ar)(Br). These data show that the major palladium complex in each case lies off of the catalytic cycle. The resting state of the reactions catalyzed by Pd(OAc) 2 andCyPF- t Bu was the palladium bis-thiolate complex [Pd(CyPF-t Bu)(SR) 2 ] (R = alkyl or aryl). The resting state in reactions catalyzed by Pd 2 (dba) 3 and CyPF- t Bu was the binuclear complex [Pd(CyPF t Bu)] 2 (μ 2 ,η 2 -dba) (9). The resting states of reactions of both aromatic and aliphatic thiols catalyzed by [Pd(CyPF- t Bu)(p-tolyl)(Br)] (3a) were the hydridopalladium thiolate complexes [Pd(CyPF- t Bu)(H)(SR)] (R= alkyl and aryl). All these palladium species have been prepared independently, and the mechanisms by which they enter the catalytic cycle have been examined in detail. These features of the reaction catalyzed by palladium and CyPF- t Bu have been compared with those of reactions catalyzed by the alkylbisphosphine DiPPF and Pd(OAc) 2 or Pd(dba) 2 . Our data indicate that the resting states of these reactions are similar to each otherand that our mechanistic conclusions about reactions catalyzed by palla dium and CyPF- t Bu can be extrapolated to reactions catalyzed by complexes of other electron-rich bisphosphines.
- Alvaro, Elsa,Hartwig, John F.
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supporting information; experimental part
p. 7858 - 7868
(2009/10/16)
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- A general, efficient, and functional-group-tolerant catalyst system for the palladium-catalyzed thioetherification of aryl bromides and iodides
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The cross-coupling reaction of aryl bromides and iodides with aliphatic and aromatic thiols catalyzed by palladium complexes of the bisphosphine ligand CyPF-tBu (1) is reported. Reactions occur in excellent yields, broad scope, high tolerance of functional groups, and with turnover numbers that exceed those of previous catalysts by 2 or 3 orders of magnitude. These couplings of bromo- and iodoarenes are more efficient than the corresponding reactions of chloroarenes and could be conducted with less catalyst loading and/or milder reaction conditions. Consequently, limitations regarding scope and functional group tolerance previously reported in the coupling of aryl chlorides are now overcome.
- Fernandez-Rodriguez, Manuel A.,Hartwig, John F.
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experimental part
p. 1664 - 1672
(2009/07/17)
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- Iron-catalyzed thioetherification of thiols with aryl iodides
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FeCl3 in combination with bisphosphine ligands represents an efficient catalyst system for the cross-coupling of aryl- and alkyl thiols with aryl iodides, a broad spectrum of functional groups can be tolerated during the catalysis. The Royal Society of Chemistry 2009.
- Wu, Jhih-Ru,Lin, Che-Hung,Lee, Chin-Fa
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supporting information; experimental part
p. 4450 - 4452
(2009/12/29)
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- ZrCl4 dispersed on dry silica gel provides a useful reagent for S-alkylation of thiols with alcohols under solvent-free conditions
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ZrCl4 which is commercially available and not a costly compound, is a relatively safe chemical [LD50 [ZrCl4, oral rat] = 1688 mg Kg]. In this report we describe the use of ZrCl4 dispersed on dry silica gel as an efficient reagent for the efficient preparation of thioethers from thiols with alcohols under solvent-free conditions.
- Firouzabadi, Habib,Iranpoor, Nasser,Jafarpour, Maasoumeh
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- The deoxygenation of sulfoxide mediated by the Ph3P/Lewis acid combination and the application to the kinetic resolution of racemic phosphines using optically active sulfoxide
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It was found that the combination of Ph3P/TiCl4 was an effective promoter for the deoxygenation of sulfoxides and gave the corresponding sulfides in good yield (up to 97%) under mild conditions. This method was applied to the reaction between racemic phosphines and (R)-methyl p-tolyl sulfoxide, and it was found that the kinetic resolution was achieved in moderate selectivities.
- Kikuchi, Satoshi,Konishi, Hiroyuki,Hashimoto, Yukihiko
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p. 3587 - 3591
(2007/10/03)
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- Carbon-sulfur bond-forming reductive elimination involving sp-, sp2-, and sp3-hybridized carbon. Mechanism, steric effects, and electronic effects on sulfide formation
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Palladium thiolato complexes [(L)Pd(R)(SR')], within which L is a chelating ligand such as DPPE, DPPP, DPPBz, DPPF, or TRANSPHOS, R is a methyl, alkenyl, aryl, or alkynyl ligand, and R' is an aryl or alkyl group, were synthesized by substitution or proton-transfer reactions. All of these thiolato complexes were found to undergo carbon-sulfur bond-forming inductive elimination in high yields to form dialkyl sulfides, diaryl sulfides, alkyl aryl sulfides, alkyl alkenyl sulfides, and alkyl alkynyl sulfides. Reductive eliminations forming alkenyl alkyl sulfides and aryl alkyl sulfides were the fastest. Eliminations of alkynyl alkyl sulfides were slower, and elimination of dialkyl sulfide was the slowest. Thus the relative rates for sulfide elimination as a function of the hybridization of the palladium-bound carbon follow the trend sp2 > sp >> sp3. Rates of reductive elimination were faster for cis-chelating phosphine ligands with larger bite angles. Kinetic studies, along with results from radical trapping reactions, analysis of solvent effects; and analysis of complexes with chelating phosphines of varying rigidity, were conducted with [Pd(L)(S-tert-butyl)(Ar)] and [Pd(L)(S- tert-butyl)(Me)]. Carbon-sulfur bond-forming reductive eliminations involving both saturated and unsaturated hydrocarbyl groups proceed by an intramolecular, concerted mechanism. Systematic changes in the electronic properties of the thiolate and aryl groups showed that reductive elimination is the fastest for electron deficient aryl groups and electron rich arenethiolates, suggesting that the reaction follows a mechanism in which the thiolate acts as a nucleophile and the aryl group an electrophile. Studies with thiolate ligands and hydrocarbyl ligands of varying steric demands favor a migration mechanism involving coordination of the hydrocarbyl ligand in the transition state.
- Mann, Grace,Baranano, David,Hartwig, John F.,Rheingold, Arnold L.,Guzei, Ilia A.
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p. 9205 - 9219
(2007/10/03)
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- Preparation of t-butyl sulfides by a novel ligand-transfer reaction of aryl thiocyanates
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Aryl t-butyl sulfides are prepared in good to excellent yields by the reaction of aryl thiocyanates with (t-Bu)2Cu(CN)Li2.
- Toste, F. Dean,Still, Ian W. J.
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p. 4361 - 4364
(2007/10/02)
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- Reactions of Thermally Generated tert-Butyl and Di(tert-alkyl)ketyl Radicals in Toluene: Cage Effects and Hydrogen Transfer
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Thermolysis of di(1-adamantyl)-tert-butylmethanol (2a) in toluene at 145-185 deg C gives mainly bibenzyl, di(1-adamantyl) ketone, di(1-adamantyl)methanol, and the cross-product, 1,1-di(1-adamantyl)-2-phenylethanol.In the presence of benzophenone (BP) or benzenethiols as hydrogen-accepting and hydrogen-donating radical scavengers, respectively, the di(1-adamantyl)methanol/di(1-adamantyl) ketone ratio tends to steady values as the scavenger/2a ratio is increased, while the cross-product disappears.At 165 deg C the secondary alcohol minimum is 8percent (BP) and the ketone minimum 11percent (thiol).These represent the contributions of geminate hydrogen atom transfer reactions to the overall yields, i.e., the cage effects.With BP the major cross-product is 1,1,2-tri-phenylethanol.Products from the self- and cross-reactions of benzyl and thiyl radicals are found when thiol is present, the diaryl disulfide predominating at high thiol concentration.In both cases, cross-products resulting from reaction of the tert-butyl radical with the scavenger-derived radical are detected in small amounts, being of greater importance in deuteriated toluene.The tert-butyl radical is considered, therefore, to be less reactive in hydrogen atom abstraction than the 1-adamantyl radical.Cage effects for other di(tert-alkyl)-tert-butylmethanols that thermolyze with exclusive t-Bu-C bond fission have also been measured and the product composition of the scavenger-free reaction interpreted by kinetic simulation based on the steady state approximation.Rate constants for hydrogen abstraction by the tert-butyl radical from toluene are not accurately determined by this procedure but seem, nevertheless, to indicate that the literature value (14.4 M-1s-1 at 48 deg C) is an overestimate. Solvent hydrogen abstraction by the ketyl radical shows a small but well-defined steric effect.
- Lomas, John S.,Briand, Sylvette,Fain, Dominique
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p. 166 - 175
(2007/10/02)
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- THIOSULFONIC S-ESTERS-III. A CONVENIENT PREPARATION OF AROMATIC SULFIDES
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The nucleophilic attack of alkyl- and aryl-lithium compounds at the sulfenyl sulfur atom in thiosulfonic S-esters performs a convenient synthesis of aromatic sulfides which are obtained cleanly and in generally excellent yields.Considering that recently we have reported a ready preparation of thiosulfonic S-esters from sulfonyl chlorides, this sulfidation reaction completes an interesting general procedure for converting the laters to any symmetrical or unsymmetrical sulfides.
- Palumbo, Giovanni,Ferreri, Carla,D'Ambrosio, Clotilde,Caputo, Romualdo
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p. 235 - 238
(2007/10/02)
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