- Kinetics of the [2+ + 4]-cycloaddition reactions of 1,3-dithian-2-ylium ions with 1,3-dienes
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The kinetics of the [2+ + 4] cycloadditions of 1,3-dithian-2-yhum ions (1) with 1,3-dienes was investigated photometrically in dichloromethane. The second-order rate constants determined for the reactions of 1 with 2,3-dimethyl-1,3-butadiene (2a) and isoprene (2b) were identical to those calculated for the first step of a stepwise cycloaddition pathway by the correlation Ig k = s (E + N). Though a concerted cycloaddition pathway is not excluded by this finding, it is obvious that the transition states of these reactions are not noticeably stabilized by the simultaneous formation of two new σ bonds.
- Mayr, Herbert,Henninger, Joachim
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- CARBON-SULPHUR BOND FORMATION CATALYSED BY BIS(DIPHENYLPHOSPHINO)-METHANE COMPLEXES OF PLATINUM(II)
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Thiols react with alkylhalides in the presence of sodium carbonate and a catalytic quantity of (dppm)PtCl2 to give thioethers.Of especial interest is the succesful application to thioacetal formation using 1,1-dihalides which, does not require the use of strong bases or the intermediacy of thiolate anions.
- Page, Philip C. Bulman,Klair, Sukhbinder S.,Brown, Michael P.,Harding, Marjoire M.,Smith, Christopher S.,et al.
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- Electrophilic Chlorine from Chlorosulfonium Salts: A Highly Chemoselective Reduction of Sulfoxides
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Herein, we describe a selective late-stage deoxygenation of sulfoxides based on a novel application of chlorosulfonium salts and demonstrate a new process using these species generated in situ from sulfoxides as the source of electrophilic chlorine. The use of highly nucleophilic 1,3,5-trimethoxybenzene (TMB) as the reducing agent is described for the first time and applied in the deoxygenation of simple and functionalized sulfoxides. The method is easy to handle, economic, suitable for gram-scale operations, and readily applied for poly-functionalized molecules, as demonstrated with more than 45 examples, including commercial medicines and analogues. We also report the results of competition experiments that define the more reactive sulfoxide and we present a mechanistic proposal based on substrate and product observations.
- Acosta-Guzmán, Paola,Mahecha-Mahecha, Camilo,Gamba-Sánchez, Diego
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supporting information
p. 10348 - 10354
(2020/07/13)
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- Selective Conversion of Carbon Dioxide to Formaldehyde via a Bis(silyl)acetal: Incorporation of Isotopically Labeled C1 Moieties Derived from Carbon Dioxide into Organic Molecules
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The conversion of carbon dioxide to formaldehyde is a transformation that is of considerable significance in view of the fact that formaldehyde is a widely used chemical, but this conversion is challenging because CO2 is resistant to chemical transformations. Therefore, we report here that formaldehyde can be readily obtained from CO2 at room temperature via the bis(silyl)acetal, H2C(OSiPh3)2. Specifically, formaldehyde is released from H2C(OSiPh3)2 upon treatment with CsF at room temperature. H2C(OSiPh3)2 thus serves as a formaldehyde surrogate and provides a means to incorporate CHx (x = 1 or 2) moieties into organic molecules. Isotopologues of H2C(OSiPh3)2 may also be synthesized, thereby providing a convenient means to use CO2 as a source of isotopic labels in organic molecules.
- Rauch, Michael,Strater, Zack,Parkin, Gerard
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supporting information
p. 17754 - 17762
(2019/11/05)
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- Reduction of CO2 into Methylene Coupled with the Formation of C-S Bonds under NaBH4/I2 System
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A selective four-electron reduction of CO2 with thiophenol using NaBH4 as a reductant is described to access dithioacetals. This reaction provides a novel synthetic method for the highly selective conversion of CO2 into methylene, and a new access to molecular structures via formation of C-S bonds using CO2 as the C1 source.
- Guo, Zhiqiang,Zhang, Bo,Wei, Xuehong,Xi, Chanjuan
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supporting information
p. 6678 - 6681
(2018/10/24)
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- Pot-economy autooxidative condensation of 2-Aryl-2-lithio-1,3-dithianes
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The autoxidative condensation of 2-aryl-2-lithio-1,3-dithianes is here reported. Treatment of 2-aryl-1,3-dithianes with n-BuLi in the absence of any electrophile leads to condensation of three molecules of 1,3-dithianes and formation of highly functionalized α-thioether ketones orthothioesters in 51-89% yields upon air exposure. The method was further expanded to benzaldehyde dithioacetals, affording corresponding orthothioesters and α-thioether ketones in 48-97% yields. The experimental results combined with density functional theory studies support a mechanism triggered by the autoxidation of 2-aryl-2-lithio-1,3-dithianes to yield a highly reactive thioester that undergoes condensation with two other molecules of 2-aryl-2-lithio-1,3-dithiane.
- Vale, Joao R.,Rimpil?inen, Tatu,Siev?nen, Elina,Rissanen, Kari,Afonso, Carlos A. M.,Candeias, Nuno R.
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p. 1948 - 1958
(2018/02/23)
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- Synthesis of 8-methylnonane-1,6,7-trien-4-one and related allenes as potentially useful synthetic precursors
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The allenic ketone 8-methylnonane-1,6,7-trien-4-one and related allenes have been synthesized from simple commercially available materials. Since allenes analogous to 8-methylnonane-1,6,7-trien-4-one have previously been transformed to substituted bicyclo[3.3.0]octanones via corresponding bicyclo[3.2.0]heptanones, it is anticipated that the present allenic ketone may also undergo similar transformations. Substituted bicyclo[3.3.0]octanones are known synthetic precursors of tricyclic sesquiterpenes. Thus, 8-methylnonane-1,6,7- trien-4-one presents itself as a possible precursor for the synthesis of tricyclopentanoid ring system present in sesquiterpenes such as hirsutene and Δ9(12)-capnellene.
- Mdachi
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experimental part
p. 103 - 113
(2012/04/23)
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- Molybdenum pentachloride (MoCl5) or molybdenum dichloride dioxide (MoO2Cl2): advanced catalysts for thioacetalization of heterocyclic, aromatic and aliphatic compounds
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A new, convenient and mild method for thioacetalization of heterocyclic, aromatic and aliphatic compounds catalyzed by MoCl5 or MoO2Cl2 is described. This novel method is important for the synthesis of the difficult to prepare heterocyclic thioacetals such as the pterin thioacetals and it offers significant advantages such as high conversion, short reaction times and simplicity in operation.
- Goswami, Shyamaprosad,Maity, Annada C.
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p. 3092 - 3096
(2008/09/20)
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- Oxalic acid catalyzed reaction between dithioacetals and acetals. A simple and eco-friendly method for a conversion of a dithioacetal to a carbonyl compound
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Oxalic acid catalyzes a reaction between dithioacetals and acetals. This reaction is useful in a new and eco-friendly method to convert dithioacetals to carbonyl compounds.
- Miyake, Hideyoshi,Nakao, Yuichi,Sasaki, Mitsuru
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p. 6247 - 6250
(2007/10/03)
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- Externally sensitized mesolytic fragmentations in dithiane-ketone adducts
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The apparent activation enthalpies, ΔH≠, for externally sensitized mesolytic fragmentations in benzophenone-dithiane adducts were obtained in variable temperature photolyses and compared with DFT activation barriers calculated for β-scission in the corresponding oxygen-centered radicals. The results of these experimental and theoretical studies further support the mechanism in which deprotonation of the hydroxy-group, in the transient cation radical, is coupled with intramolecular electron transfer furnishing the O-centered radical, which subsequently fragments. The quantum yields of fragmentation increase for higher alkyl substituted dithiane adducts.
- Gustafson, Tiffany P.,Kurchan, Alexei N.,Kutateladze, Andrei G.
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p. 6574 - 6580
(2007/10/03)
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- Ionic liquid as catalyst and reaction medium: A simple, convenient and green procedure for the synthesis of thioethers, thioesters and dithianes using an inexpensive ionic liquid, [pmIm]Br
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An easily accessible and inexpensive room temperature ionic liquid, 1-pentyl-3-methylimidazolium bromide, [pmIm]Br efficiently catalyzes the reaction of alkyl halides or acyl halides with thiols without any solvent at room temperature leading to the synthesis of thioethers and thioesters in high yields. This reaction has also been extended for the preparation of dithianes and transthioetherification. The ionic liquid is recovered and recycled for subsequent runs.
- Ranu, Brindaban C.,Jana, Ranjan
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p. 1811 - 1818
(2007/10/03)
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- Direct transformation of 1,3-dihalides into dithianes and dithiepines via a novel one-pot reaction with carbon disulfide and sodium borohydride
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1,3-Dithianes and -dithiepines are prepared via an experimentally simple and efficient direct transformation of 1,n-alkyl dihalides utilizing carbon disulfide and sodium borohydride.
- Wan, Yongqin,Kurchan, Alexei N.,Barnhurst, Loren A.,Kutateladze, Andrei G.
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p. 1133 - 1135
(2007/10/03)
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- Catalytic Thioether and Thioacetal Formation using Bis(diphenylphosphino)methane Complexes of Platinum (II)
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Bis(dihenylphosphino)methane complexes of platinum (II) catalyze the formation of thioethers from thiols and alkyl halides and of thioacetals from thiols or dithiols and geminal dihalides.
- Page, Philip C. Bulman,Klair, Sukhbinder S.,Brown, Michael P.,Smith, Christopher S.,Maginn, Stephen J.,Mulley, Suzanne
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p. 5933 - 5940
(2007/10/02)
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- CLAY CATALYSIS: SYNTHESIS OF ORGANOSULPHUR SYNTHONS
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The Montmorillonite KSF catalyses the synthesis of a large variety of organic sulphur compounds from carbonyl compounds: dithianes, thioacetals, thioketals,thiochromanes.
- Labiad, B.,Villemin, D.
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- STUDY OF THE ANOMERIC EFFECT IN 2-SUBSTITUTED 1,3-DITHIANES
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The conformational analysis of several 2-substituted 1,3-dithianes made possible the evaluation of S-C-Y anomeric interactions, where Y=SCH3,SC6H5,CO2CH3,COC6H5,CO2H and N(CH3)2.The relative magnitude of the effects observed for these groups odithiane(Y)-ΔGocyclohexane(Y)> can be explained in terms of the combined influence of dipole/dipole and two-electron stabilizing interactions (stereoelectronic effect).
- Juaristi, Eusebio,Tapia, Josefina,Mendez, Rodolfo
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p. 1253 - 1264
(2007/10/02)
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- 1,3-Dithienium- and 1,3-Dithiolenium Salts, V. Determination of the Relative Reactivity of 1,3-Dithian-2-ylium Tetrafluoroborates by Intermolecular Hydride Ion Transfer
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The 1,3-dithienium- and 1,3-dithiolenium tetrafluoroborates 4 (n=3, 2) react in good yields with the (trimethylsiloxy)alkenes 3 available from β-dicarbonyl compounds to give the 2-substituted 1,3-dicarbonyl compounds 5.Owing to the formation of the difluoroboron acid esters 8 as competition products 3 has to be employed in excess, however.Reaction of 4 (n=3) with 1,3,5-cycloheptatriene (10) leads to the 1,3-dithianes 11 and the more stable tropylium tetrafluoroborate (12).The determination of the corresponding rates of reduction allows in a simple manner the ascertainment of the relative reactivities of 4.Whereas the reactivities of the aryl-substituted representatives of 4 show a sufficient correlation corresponding to the Hammett relationship, the variations of the reactivities of the alkyl substituted salts 4 can be explained on the basis of hyperconjugative stabilization.
- Stahl, Ingfried
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p. 4857 - 4868
(2007/10/02)
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- RADICAL CATIONS OF ORGANIC SULPHIDES AND DISULPHIDES FORMED BY RADIOLYSIS: AN ELECTRON SPIN RESONANCE STUDY
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Exposure of dilute solutions of various organic sulphides in fluorotrichloromethane at 77 K to 60Co γ-rays gave species identified by their e.s.r. spectra as the parent radical cations.The average β-proton coupling (R2CHS.R)+ of ca. 20 G is about half that for the corresponding ether cations, indicating greatly reduced ?-? delocalisation.However, the spread of g-values (ca. 2.032, 2.015, 2.00) is much greater than that for the ether cations.These cations readily react with other disulphide molecules to form (R2S.-SR2)+ dimer cations.The spectrum for tetrahydrothiophene (tetramethylene sulphide) exhibits a large coupling to two axial protons (ca. 42 G) and two equatorial protons (ca. 19 G), the coupling constants again being about half those for tetrahydrofuran cations.However, conformational inversion did not occur below the softening point of the solids (ca. 160 K) in marked contrast with the ether cations.The three-and four-membered ring cations (ethylene and trimethylene sulphide cations) gave very similar spectra with gx = gy, and four equivalent protons having an isotropic coupling of ca. 31 G.Thus their structures are similar to the normal R2S.+ cations, the equivalence of the g-values being interpreted in terms of effective C-S-C bond angles (θ) close to 90 deg.This, in turn, implies that θ > 90 deg for the unconstrained cations.It is noteworthy that the ethylene oxide (oxirane) cation exhibits a smaller coupling to its four protons (16 G).This implies a drastic change in structure for the oxirane cation which is clearly not the case for the sulphur analogue.Disulphides of structure R-S-CH2-S-R form cyclic ?* radicals with weak S-S bonding, in marked contrast with the oxygen analogues (acetal cations) which have ?-structures conferring very high spin-density onto the CH2 protons.Other molecules containing two RSR units form similar cyclic ?* radicals.Persulphides of structure RS-SR readily give the ?-cations (RS.SR)+, characterised by g-values in the region of 2.035, 2.018, 2.002.The smaller range of g values for (PhS.-SPh)+ cations is interpreted in terms of ca. 30percent spin-delocalisation into both the benzene rings.
- Rao, Ramakrishna D. N.,Symons, M. C. R.,Wren B. W.
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p. 1681 - 1688
(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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- 1,3-Dithiane derivatives as radioprotective agents
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Compounds derived from 1,3 dithiane have been prepared and evaluated as potential antiradiation agents in mice. They are generally less toxic than their dithiolane homologs and have markedly lower radioprotective activity.
- Fernandez,Robbe,Chapat,et al.
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p. 461 - 464
(2007/10/02)
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- THE USE OF METALLOIDS (-SiMe3,-SnR3) AS PROTECTED CARBANIONS; SELECTIVE ACTIVATION AND NEW CYCLIZATION PROCESSES
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Two aspects of organosilicon and -tin chemistry will be dealt with in this paper: the reactivity of allylmetalloids and the potential of the C-MR3 function as a protected carbanion which can be unmasked to provide synthetically useful carbon nucleophiles with the primary focus on the latter.
- Andarsen, Niels H.,McCrae, David A.,Grotjahn, Douglas B.,Gabhe, Satish Y.,Theodore, Louis J.,et al.
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p. 4069 - 4079
(2007/10/02)
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