- Photosensitized cleavage of the dithio protecting group by visible light
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Dithio derivatives of aldehydes and ketones have been deprotected under neutral conditions using visible light provided by a 120 Watt spotlight and methylene green as a sensitizer. The key step in the deprotection is apparently an electron transfer from the dithio derivative to the electronically excited visible dye. The resulting dithio radical cation undergoes fragmentation, and the corresponding aldehydes and ketones are isolated in excellent yields.
- Epling, Gary A.,Wang, Qingxi
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Read Online
- 3-(2-aminophenyl)-4-methyl-1,3-thiazole-2(3H)-thione as an ecofriendly sulphur transfer agent to prepare alkanethiols in high yield and high purity
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A new process is described for preparing very pure linear alkanethiols and linear α,ω-alkanedithiols using a sequential alkylation of the title compound, followed by a ring closure to quantitatively give the corresponding 3-methyl[1,3]thiazolo[3,2-a]-[3,1
- Mehdid, Mohammed Amine,Djafri, Ayada,Roussel, Christian,Andreoli, Federico
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experimental part
p. 4634 - 4643
(2010/04/06)
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- Reduction of thiokols in the system hydrazine hydrate-base as a new route to alkanedithiols
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A new procedure for preparative synthesis of alkanedithiols from simple commercially available products is based on reduction of the S-S bond in appropriate polyalkylene disulfides (thiokols) in the system hydrazine hydrate-base. Thiokols were prepared by reaction of dihaloalkanes with Na2S2 or K2S2 generated from elemental sulfur and alkali in aqueous hydrazine hydrate. Reaction of 1,2-dibromocyclohexane with sodium or potassium disulfide yields bis(2-bromocyclohexyl) sulfide as the only product.
- Alekminskaya,Russavskaya,Korchevin,Deryagina,Trofimov
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p. 732 - 737
(2007/10/03)
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- Reduction of thiocols to alkanepolythiols with benzeneselenol
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Heating of benzeneselenol with polymethylene disulfides to 40-120°C results in formation of the corresponding alkanedithiols or alkanetrithiols and diphenyl diselenide. Poly(tetramethylene disulfide) reacts with benzeneselenol to give 1,2-dithiane and diphenyl diselenide. A radical mechanism of this reaction is discussed.
- Shilkina,Papernaya,Deryagina
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p. 263 - 265
(2007/10/03)
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- Synthesis of thiols via palladium catalyzed methanolysis of thioacetates with borohydride exchange resin
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Various thiols are prepared quantitatively from the corresponding thioacetates via Pd catalyzed methanolysis with borohydride exchange resin under a mild and neutral conditions. One-pot synthesis of thiols from alkyl halides through the formation of alkyl thioacetates using thioacetate exchange resin followed by methanolysis is also described.
- Choi,Yoon
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p. 2655 - 2663
(2007/10/02)
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- Kinetics of Hydrolysis of 2-Aryl-2-phenyl-1,3-dithianes in 10percent (v/v) Dioxane-Water, Containing Perchloric Acid. Acidity Functions in this Solvent and the Reactivity of α-Thio Carbocations
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The acid-catalysed hydrolysis of 2-aryl-2-phenyl-1,3-dithianes in 10percent (v/v) dioxane-water occurs at a convenient rate at 25 deg C in the presence of 5-8 mol dm-3 perchloric acid.The effect on the rate of changes in substituents, acidity and temperature, and of the use of a deuteriated solvent are described.Measurements of the H0 and X acidity functions for the solvent are reported; their values are very similar to those found for pure water over most of the acidity range.The mechanism of hydrolysis is believed to change from an ASE2 scheme for the most reactive dithianes to an A2-like scheme for the least reactive.In very concentrated acid solutions the dithianes (and other suitable S,S-acetals) lead to stoichiometric amounts of the α-thio carbocations often postulated as low-concentration intermediates in S,S-acetal hydrolysis.The kinetics of the reaction of these ions with water to give the benzenophenone (or corresponding carbonyl compound) are described, and compared with findings for similar α-oxo carbocations.Previous views on the mechansim of this reaction are criticised.
- Ali, Muhammad,Satchell, Derek P. N.,Le, Vu T.
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p. 917 - 922
(2007/10/02)
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- Identification of an ASE2 Mechanism in the Hydrolysis of Cyclic Thioacetals
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2-Phenyl-2-methyl-1,3-dithiane and its p-methoxy derivative undergo hydrolysis in concentrated aqueous perchloric acid via the ASE2 mechanism rather than via the A1 mechanism.
- Ali, Muhammad,Satchell, Derek P. N.
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p. 866 - 867
(2007/10/02)
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- Degenerate intermolecular thiolate-disulfide interchange involving cyclic five-membered disulfides is faster by ～103 than that involving six- or seven-membered disulfides
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The rate constants for degenerate intermolecular thiolate-disulfide interchange involving 1,2-dithiolane (S(CH2)3S) are higher than those involving 1,2-dithiane (S(CH2)4S) by a factor of ～650 in mixtures of DMSO-d6 and D2O. The extrapolated rate constant for 1,2-dithiolane in DMSO-d6 is fast (k ～ 108 M-1 s-1). The rate constants for cyclic six- and seven-membered disulfides are similar to those for acyclic disulfides. Rate constants for self-exchange were measured by dynamic 1H NMR line-shape analysis. The evolutionary selection of lipoamide as the cofactor in 2-oxo acid dehydrogenases may reflect the fast rate of ring opening of the dithiolane ring by nucleophiles.
- Singh, Rajeeva,Whitesides, George M.
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p. 6304 - 6309
(2007/10/02)
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- Acid-Catalyzed Hydrolysis of a (γ-Hydroxyalkyl)ketene Dithioacetal. A Cyclic Intermediate and Product Distribution
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2-(Hydroxyalkylidene)-1,3-dithiane 1a undergoes acid-catalyzed hydrolysis.Disappearance of 1a is faster than formation of the products thio ester 5a and lactone 5a'.The product distribution changes with pH in a similar way to that of hydrolysis of the cyclic intermediate 3a.Hydrolysis of 1a must proceed mostly through 3a, accompanying its accumulation.In comparison with the reference substrate 1b, anchimeric assistance by the internal hydroxyl group was not observed in wholly aqueous solution, but it becomes apparent in aqueous acetonitrile solutions at high organic concentration.Neighboring hydroxyl participation is considered to occur by internal solvation, and the carbocation 2a can exist as a discrete intermediate of the hydrolysis.
- Okuyama, Tadashi,Fueno, Takayuki
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p. 1405 - 1408
(2007/10/02)
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- Kinetics and Mechanism of the Metal Ion-promoted Hydrolysis of 2-Phenyl-1,3-dithiane in Aqueous Dioxane Solution
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In 1percent (v/v) aqueous dioxane the hydrolysis of 2-phenyl-1,3-dithiane (1) is promoted by thallium (III), mercury(II), mercury(I), and silver(I) ions; the qualitative sequence of their efficiencies is Tl3+>/=Hg2+>Hg22+>Ag+.Kinetic studies suggest the reaction mechanism with the thallium and mercury ions involves the rapid formation of a 1:1-adduct between the metal ion and the dithiane (formation constant, K 54.5, 3.0E4,and 630 dm3 mol-1 for Tl3+, Hg2+, and Hg22+, respectively at 25 deg C) followed by a slow ring-opening step (k2 77, 0.20 and 0.07 s-1, respectively) which may not involve water.Added chloride ions inhibit the mercury(II) ion promotion: HgCl+ and HgCl2 have, respectively, ca. 90percent and ca. 14percent of the reactivity of Hg2+.An increase in the dioxane content of the solvent to 20percent (v/v) has relatively little effect on the reaction.The general kinetic pattern, and level of reactivity, is similar to that observed previously for the Tl3+- and Hg2+-promoted hydrolysis of 2-phenyl-1,3-dithiolane (4).Both (1) and (4) are less basic towards Tl3+ than towards Hg2+, and the thallium adducts of (1) and (4) both react more rapidly than the corresponding Hg2+ adducts.However, (1) is less basic than (4) towards Tl3+, whereas the reverse is true for Hg2+, and the Tl3+ adduct of (1) is more reactive than that of (4), whereas the reverse is true of the reactivities of the corresponding Hg2+ adducts.These differences of detail suggest that the (unknown) conformations of the adducts control to some extent the values of K and k2.
- Satchell, Derek P. N.,Satchell, Rosemary S.
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p. 513 - 516
(2007/10/02)
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- A NEW ROUTE TO 1-PHENYLNAPHTHALENES BY CYCLOADDITION: A SIMPLE AND SELECTIVE SYNTHESIS OF SOME NAPHTHALENE LIGNAN LACTONES
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2-(2-Dithianyl)benzhydrols (2 a-c) undergo facile cycloaddition reaction with maleic anhydride under thermal conditions to give 1-phenyl-naphthalenes (7 a-c) in one step.The naphthalenes (7 a-c) have been converted into the naphthalene lignan lactones, (9 a-c) and (10 a-c).
- Takano, Seiichi,Otaki, Shizuo,Ogasawara, Kunio
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p. 1659 - 1660
(2007/10/02)
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- CONVERSION OF CYCLIC TRITHIOCARBONATES TO THIOACETALS, INCLUDING 1,3-DITHIANE, BY REDUCTION WITH DIISOBUTYLALUMINIUM HYDRIDE (DIBAL)
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Cyclic trithiocarbonates can be desulfurized with diisobutylaluminium hydride (DIBAL) to form the corresponding thioacetals.This new synthetic pathway was exploited for the preparation of several Umpolung reagents, including 1,3-dithiane.An efficient isolation of sodium trithocarbonate is described.
- Jordis, Ulrich,Rudolf, Manfred
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p. 279 - 284
(2007/10/02)
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- Development of a Strategy for Convergent Total Synthesis of the Aureolic Acid Antitumor Antibiotics
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It has been found that condensation of an o-toluate carbanion with a 3-alkoxycyclohexen-2-one will produce the dihydroanthracenone system found in olivin (3) and chromomycinone (4), the aglycons of the aureolic acids.Several examples of this reaction are described, leading to synthesis of model aromatic systems 17, 18, 21, 23, 24, and 26.A route to compound 34, having the complete carbon framework and most of the functionality of olivin, has been developed which uses the above type of condensation as the critical step.
- Dodd, John H.,Garigipati, Ravi S.,Weinreb, Steven M.
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p. 4045 - 4049
(2007/10/02)
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- Rate Constants and Equilibrium Constants for Thiol-Disulphide Interchange Reactions Involving Oxidized Glutathione
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The rate of reduction of oxidized glutathione (GSSG) to glutathione (GSH) by thiolate (RS-) follows a Broensted relation in pKas of the conjugate thiols (RSH): βnuc ca. 0.5.This value is similar to that for reduction of Ellman's reagent: βnuc ca. 0.4 - 0.5.Analysis of a number of rate and equilibrium data, taken both from this work and from the literature, indicates that rate constants, k, for a range of thiolate-disulphide interchange reactions are correlated well by equations of the form log k = C + βnucpKanuc + βcpKac + βlgpKalg ( nuc = nucleophile, c = central, and lg = leaving group sulfur): eq 36 - 38 give representative values of the Broensted coefficients.The values of these Bronsted coefficients are not sharply defined by the available experimental data, although eq 36 - 38 provide useful kinetic models for rates of thiolate-disulfide interchange reactions.The uncertainty in these parameters is such that their detailed mechanistic interpretation is not worthwhile, but their qualitative interpretation - that all three sulphur atoms experience a significant effective negative charge in the transition state, but that the charge is concentrated on the terminal sulfurs - is justified.Equilibrium constants for reduction of GSSG using α,ω-dithiols have been measured.The reducing potential of the dithiol is strongly influenced by the size of the cyclic disulfide formed on its oxidation: the most strongly reducing dithiols are those which can form six-membered cyclic disulfides.Separate equilibrium constants for thiolate anion-disulphide interchange (KS-) and for thiol-disufide interchange (KSH) have been estimated from literature data: KS- is roughly proportional to 2ΔpKa is the difference between the pKas of the two thiols involved in the interchange.The contributions of thiol pKa values to the observed equilibrium constants for reduction of GSSG with α,ω-dithiols appear to be much smaller than those ascribable to the influence of structure on intramolecular ring formation.These equilibrium and rate constants are helpful in choosing dithiols for use as antioxidants in solutions containing proteines: dithiothreitol (DTT), 1,3-dimercapto-2-propanol (DMP), and 2-mercaptoethanol have especially useful properties.
- Szajewski, Richard P.,Whitesides, George M.
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p. 2011 - 2026
(2007/10/02)
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- Ethylenic silicon compounds and thermoplastic elastomers obtained therefrom
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The invention provides organosilicon compounds of the formula: STR1 in which: N IS 1, 2 OR 3; Each R, which may be identical or different, is a monovalent organic group which contains a carbon-carbon double bond and from 2 to 10 carbon atoms; Each R1, which may be identical or different, is a straight or branched alkyl radical optionally substituted by one or more halogen atoms or cyano groups; an aryl radical or an alkylaryl radical optionally substituted by one or more halogen atoms; R2 is a straight or branched divalent alkylene or alkylidene radical possessing up to 4 carbon atoms; X is a divalent radical consisting of, or containing, at least one hetero-atom selected from oxygen, sulphur and nitrogen atoms, the radical being attached to the radical R2 via a said hetero-atom; G is an organic radical of valency (m+ l) possess from 1 to 30 carbon atoms; m is 1, 2 or 3; And each Y, which may be identical or different, is a functional group selected from: --NO2, STR2 --COOM (where M represents a sodium, potassium or lithium atom); --COOR4 ; STR3 --COCl; --OH; --OR4 ; STR4 --SH; --SR4 ; STR5 --CONH2 ; --CSNH2 ; --CN; --CH2 --NH2 ; --CHO; STR6 --NCO; STR7 wherein R3 represents a hydrogen atom or a straight or branched alkyl radical possessing up to 6 carbon atoms and R4 represents an alkyl radical possessing up to 4 carbon atoms, with the proviso that two Y groups can together constitute an imide group STR8 wherein R5 represents a hydrogen atom or a straight or branched alkyl radical possessing up to 4 carbon atoms. These are useful intermediates in the preparation of disilanes and silicon polymers, in particular of polyethylenic silicon compounds which can be polymerized with an α, ω-dihydrogenopolysiloxane to give thermoplastic elastomers.
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