- Benzylic Thio and Seleno Newman-Kwart Rearrangements
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The thermally induced OBn → SBn and OBn → SeBn migration reactions facilitate the rearrangement of O-benzyl thio- and selenocarbamates [BnOC(=X)NMe2] (X = S or Se) into their corresponding S-benzyl thio- and Se-benzyl selenocarbamates [BnXC(=O)NMe2] (X = S or Se). A series of substituted O-benzyl thio- and selenocarbamates were synthesized and rearranged in good yields of 33-88%. The reaction rates are higher for substrates with electron-donating groups in the 2 or 4 position of the aromatic ring, but the rearrangement also proceeds with electron-withdrawing substituents. The rearrangement follows first-order reaction kinetics and proceeds via a tight ion pair intermediate consisting of the benzylic carbocation and the thio- or selenocarbamate moiety. Computational studies support these findings.
- Eriksen, Kristina,Ulfkj?r, Anne,S?lling, Theis I.,Pittelkow, Michael
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p. 10786 - 10797
(2018/09/06)
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- Nonenzymatic Dynamic Kinetic Resolution of in situ Generated Hemithioacetals: Access to 1,3-Disubstituted Phthalans
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The first nonenzymatic DKR reaction of hemithioacetals is developed. Hemithioacetals were formed in situ via thiol addition and subsequently underwent an intramolecular oxa-Michael reaction. The scope of the reaction was quite broad ranging from aliphatic to aromatic substituents and 1,3-disubstituted-1,3-dihyroisobenzofuran products were obtained in good yields with moderate diastereoselectivities and high enantioselectivities. (Figure presented.).
- Nath, Utpal,Chowdhury, Deepan,Pan, Subhas Chandra
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p. 1628 - 1633
(2018/03/21)
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- Novelties of selective triphasic synthesis of bis-(p-chlorobenzyl) sulfide using hydrogen sulfide and reusable phase transfer catalyst
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The present investigation is based on the advancement in hydrogen sulfide (H2S) capture and utilization (HSCU). Commercially H2S is absorbed efficiently using alkanolamines such as methyldiethanolamine (MDEA). Aqueous H2S-rich MDEA is proposed to act as a sulfiding agent for aromatic halides such as p-chlorobenzyl chloride (p-CBC) to synthesize value-added thioethers. The objective of the present investigation is to synthesize bis-(p-chlorobenzyl) sulfide (BPCBS), a value-added thioether, selectively using p-CBC and H2S-laden aqueous MDEA. For the immiscible bi-phasic system, reusable solid phase transfer catalyst, polymer-bound tributylmethylammonium chloride (PBTBMAC) was employed under liquid-liquid-solid (L-L-S) mode in the presence of solvent toluene to enhance the reaction rate and product selectivity. Full conversion of p-CBC was obtained with 100% selectivity towards the desired product BPCBS at optimized specific level of process parameters. The catalyst has shown substantial activity even after three times of reuse, which leads to waste minimization and economic benefits. A generalized empirical kinetic model was developed and successfully validated against the experimental results. The triphasic reaction thus leads to process intensification, waste minimization and selectivity enhancement. The process can be utilized as an alternative to many other HSCU processes to utilize the sour gas in synthesizing value-added chemicals.
- Jha, Preeti,Mondal, Ujjal,Gogoi, Devipriya,Singh, Gaurav,Sen, Sujit
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- Thiobencarb degradation by TiO2 photocatalysis: Parameter and reaction pathway investigations
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The present study deals with the photocatalytic degradation of the thiocarbamate herbicide, thiobencarb (TBC), in the presence of TiO2 particles and UV-A (λ = 365 nm) radiation. Results show rapid and complete oxidation of TBC after 90 min, and slightly over 70% of TBC was mineralized after 32-h treatment. Factors such as solution pH, TiO2 dosage, and the presence of anions are found to influence the degradation rate. The establishment of the reaction pathway is made possible by a thorough analysis of the reaction mixture identifying the main intermediate products generated. Results suggest that possible transformation pathways may include hydroxylation, dealkylation and C-S bond cleavage processes. The possible degradation pathways are proposed and discussed on the basis of the evidence of oxidative intermediate formation.
- Lai, Hsiao-Fang,Chen, Chiing-Chang,Wu, Ren-Jang,Lu, Chung-Shin
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experimental part
p. 87 - 97
(2012/07/28)
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- Preparation and in-vitro evaluation of 4-benzylsulfanylpyridine-2- carbohydrazides as potential antituberculosis agents
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A set of 4-benzylsulfanylpyridine-2-carbohydrazides was synthesized and evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, non-tuberculous mycobacteria, and multidrug-resistant M. tuberculosis. The activities expressed as the minimum inhibitory concentration (MIC) fall into a range of 2 to 125 μmol/L, most often 4 to 32 μmol/L. The results revealed that the substituents on the benzyl moiety do not influence the antimycobacterial efficacy. The substances exhibited similar activities against sensitive and resistant strains of M. tuberculosis. Furthermore, compounds show low antiproliferative effect and cytotoxicity.
- Herzigova, Petra,Klimesova, Vera,Palat, Karel,Kaustova, Jarmila,Dahse, Hans-Martin,Moellmann, Ute
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body text
p. 394 - 404
(2009/11/30)
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- Thioacetate deprotection
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A method of thioacetate deprotection by providing a compound of the formula R1—S—CO—R2, and reacting the compound with a quaternary ammonium cyanide salt in the presence of a protic solvent in an inert atmosphere to convert the compound to a product of the formula R1—SH. R1 is an organic group in which the bonding to sulfur is through a saturated carbon, and R2 is an aliphatic group.
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- Electron transfer to sulfides and disulfides: Intrinsic barriers and relationship between heterogeneous and homogeneous electron-transfer kinetics
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The electron-acceptor properties of series of related sulfides and disulfides were investigated in N,N-dimethylformamide with homogeneous (redox catalysis) and/or heterogeneous (cyclic voltammetry and convolution analysis) electrochemical techniques. The electron-transfer rate constants were determined as a function of the reaction free energy and the corresponding intrinsic barriers were determined. The dependence of relevant thermodynamic and kinetic parameters on substituents was assessed. The kinetic data were also analyzed in relation to corresponding data pertaining to reduction of diaryl disulfides. All investigated reductions take place by stepwise dissociative electron transfer (DET) which causes cleavage of the Calkyl-S or S-S bond. A generalized picture of how the intrinsic electron-transfer barrier depends on molecular features, ring substituents, and the presence of spacers between the frangible bond and aromatic groups was established. The reduction mechanism was found to undergo a progressive (and now predictable) transition between common stepwise DET and DET proceeding through formation of loose radical anions. The intrinsic barriers were compared with available results for ET to several classes of dissociative- and nondissociative-type acceptors, and this led to verification that the heterogeneous and the homogeneous data correlate as predicted by the Hush theory.
- Meneses, Ana Belen,Antonello, Sabrina,Arevalo, Maria Carmen,Gonzalez, Concepcion Carmen,Sharma, Jadab,Wallette, Andrea N.,Workentin, Mark S.,Maran, Flavio
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p. 7983 - 7995
(2008/04/01)
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- Aliphatic thioacetate deprotection using catalytic tetrabutylammonium cyanide
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A series of thiol-functionalized organic compounds were selected to analyze the scope and efficiency of a new thioacetate deprotection method using catalytic tetrabutylammonium cyanide (TBACN) to effect the transformation of a thioacetate group to a free thiol in the presence of a protic solvent. Particularly attractive are the mild reaction and workup conditions, reduced byproduct formation typically seen using literature methods and yields of greater than 80% for the free aliphatic thiols. This method is effective on aliphatic thiols with trityl, benzyl, p-halo-benzyl, phenethyl, phenoxyethyl, and cyclohexylethyl structural moieties, but it is not effective with thiophenols.
- Holmes, Brian T.,Snow, Arthur W.
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p. 12339 - 12342
(2007/10/03)
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- Chemoselective protection of thiols versus alcohols and phenols. The Tosvinyl group
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The conjugate addition of aliphatic and aromatic thiols to ethynyl p-tolyl sulphone (tosylacetylene) has been managed to afford Tosvinyl derivatives chemoselectively (in the presence of oxygen nucleophiles) and stereoselectively (isomers Z) in practically quantitative yields. The conditions of choice are: catalytic amounts of Et3N (only 0.5-1.0 mol%), a reaction temperature around 0°C and, for the less acidic thiols, CF3CH2OH or CH3CN/CF3CH2OH as the solvent. Thus, N-Boc-Cys-OMe has been quantitatively protected as its S-Tosvinyl derivative in the presence of N-Boc-Ser-OMe and N-Boc-Tyr-OMe. This novel protecting group is stable to several basic and acidic conditions; its removal is achieved at rt by treatment with an excess of pyrrolidine or at 0°C with alkanethiolate ions.
- Arjona, Odón,Medel, Rocío,Rojas, Jenny,Costa, Anna M.,Vilarrasa, Jaume
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p. 6369 - 6373
(2007/10/03)
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- Solid Supported Reagents and Reactions. Part 21.1 Rapid and Clean Synthesis of Thiols from Halides Using Polymer-supported Hydrosulfide
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A variety of thiols are prepared from corresponding halides using polymer-supported hydrosulfide in excellent yields. Isolation of pure products by simple filtration and evaporation is an important feature of this method.
- Bandgar, Babasaheb P.,Pawar, Sanjay B.
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p. 212 - 213
(2007/10/03)
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- Mechanism of the Solution-Phase Reaction of Alkyl Sulfides Atomic Hydrogen. Reduction via a 9-S-3 Radical Intermediate
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The low selectivity of benzyl alkyl sulfide fragmentation subsequent to its reaction with atomic hydrogen is indicative of a reaction that proceeds via an early transition state. The competitive reduction of a series of substituted-benzyl alkyl sulfides was insensitive to the substituent on the aromatic ring (ρ = -0.13, r = 0.99). The relative rates of fragmentation of a series of the substituted-benzyl alkyl sulfides gave a V-shaped Hammett plot. Both electron-donating and electron-withdrawing groups destabilized the transition state (ρ = +0.99, r = 0.999; ρ = -0.82, r = 0.992). Since the relative rates of disappearance of the alkyl benzyl sulfides are not substituent dependent, but the relative rates of fragmentation are, a 9-S-3 intermediate is preferred as the structure leading to products.
- Tanner, Dennis D.,Koppula, Sudha,Kandanarachchi, Pramod
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p. 4210 - 4215
(2007/10/03)
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- NO-Group transfer (transnitrosation) between S-nitrosothiols and thiols. Part 2
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The kinetics of NO-group transfer have been measured for the reaction between a nitrosothiol (HOCH2CH2SNO) and nine thiols, mostly based on the cysteine structure.The reaction is second-order and there is evidence for a steric effect for thiols containing 1,1-dimethyl substituents (penicillamine derivatives).Reaction occurs via the thiolate anion as shown by the pH-rate constant profile, and a full kinetic analysis for the reactions of two thiols (N-acetylcysteine and glutathione) is quantitatively in agreement with this mechanism.Variation of the nitrosothiol structure for reaction with N-acetylcysteine shows that electron-withdrawing substituents in the nitrosothiol promote reaction; there is a similarity with the corresponding reactions of alkyl nitrites.
- Barnett, D.Jonathan,Rios, Ana,Williams, D. Lyn H.
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p. 1279 - 1282
(2007/10/03)
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- Synthesis and Biological Activity of trans-(+/-)-N-Methyl-2-(3-pirydyl)-2-tetrahydrothiopyrancarbothioamide 1-Oxide (RP 49356) and Analogues: A New Class of Potassium Channel Opener
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The synthesis and biological activity of trans-(+/-)-N-methyl-2-(3-pyridyl)-2-tetrahydrothiopyrancarbothioamide 1-oxide (8a, RP 49356) and analoques is reported.These compounds constitute a new structural class of K+-channel opener.The effects of changes in the pyridyl group, thioamide, and thiane ring on in vitro K+-channel opening activity are discussed.A 3-pyridyl or 3-quinolyl group, a small N-alkyl thioamide function, and a thiane oxide ring, in which the sulfoxide is in a trans relationship to thioamide, are preferred for activity.Selected compounds were tested intravenously in the normotensive anaesthetized rat for hypotensive effects, and the activities reflect their in vitro K+-channel opening activity.This led to further evaluation of compound 8a and the selection of the (-)-enantiomer 8b (RP 52891) for development as an antihypertensive and antianginal agent.
- Brown, Thomas J.,Chapman, Robert F.,Cook, David C.,Hart, Terance W.,McLay, Iain M.,et al.
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p. 3613 - 3624
(2007/10/02)
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- ONE POT CONVERSION OF ALKYL HALIDES INTO THIOLS UNDER MILD CONDITIONS
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Alkyl halides are converted into the corresponding thiols in good yields at room temperature under neutral conditions by reaction with 1-(2-hydroxyethyl)-4,6-diphenylpyridine-2-thione.
- Molina, P.,Alajarin, M.,Vilaplana, M. J.,Katritzky, A. R.
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p. 469 - 472
(2007/10/02)
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