- NOVEL HETEROARYL-TRIAZOLE COMPOUNDS AS PESTICIDES
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The present invention relates to novel heteroaryl-triazole compounds of the general formula (I), in which the structural elements X, R1, R2, R3, R4 and R5 have the meaning given in the description, to
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Page/Page column 137
(2021/06/04)
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- A divergent synthesis of oligoarylalkanethiols with Lewis-basic N-donor termini
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Araliphatic thiols are key molecules for the formation of self-assembled monolayers with high long-range order. If these monolayers shall act as bases for the attachment of other molecules, the respective thiols need to carry suitable functional groups, such as the amino or the pyridine group. Due to their Lewis-basicity, these groups are not compatible with the thiol group under most reaction conditions. Here, an entry into this versatile class of compounds is presented, by using fundamental building blocks in which the thiol groups are protected as triisopropylsilyl sulfides making them compatible with many reagents including Grignard reagents and palladium catalysts. With this strategy at hand, six thiols with bi- and terphenyl backbones, one to three methylene groups, and amino or pyridine head groups became accessible in short reaction sequences. The Royal Society of Chemistry 2010.
- Schuepbach, Bjoern,Terfort, Andreas
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scheme or table
p. 3552 - 3562
(2010/08/21)
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- The mechanism of polarity-reversal catalysis as involved in the radical-chain reduction of alkyl halides using the silane-thiol couple
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The mechanism by which thiols promote the radical-chain reduction of alkyl halides by a variety of simple silanes, such as Et3SiH and Ph3SiH, has been investigated in detail. Kinetic studies of the thiol-catalysed reduction of 1-bromooctane and of 1-chlorooctane by Et3SiH in cyclohexane at 60°C are consistent with a mechanism that involves reversible abstraction of hydrogen by the thiyl radical from the silane, followed by abstraction of halogen from the octyl halide by the resulting triethylsilyl radical and quenching of the derived octyl radical by the thiol to give octane. On the basis of this mechanism, rate constants for abstraction of hydrogen from Et3SiH by the adamantane-1-thiyl radical (kXSH) and for transfer of hydrogen in the reverse direction (KSiH) were determined as 3.2 × 104 M-1 s-1 and 5.2 × 107 M-1 s-1, respectively, at 60°C. The equilibrium constant kXSH/kSiH is thus 6.2 × 10-4 at 60°C and corresponds to ΔrH ≈ ΔrG = +20.4 kJ mol-1 for abstraction of hydrogen from Et3SiH by 1-AdS, implying that the Si-H bond in the silane is stronger by ca. 20 kJ mol-1 than the S-H bond in the alkanethiol. The silanethiol (ButO)3SiSH was found to be a more effective catalyst than 1-AdSH, because kXSH is greater (1.3 × 105 M-1 s-1) while kSiH is very similar (5.1 × 107 M-1 s-1). The value of kXSH/kSiH is now 2.6 × 10-3 at 60°C and thus the S-H bond in this silanethiol is stronger by ca. 4 kJ mol-1 than that in 1-AdSH. The proposed mechanism for alkyl halide reduction is strongly supported by kinetic studies of the thiol-catalysed H/D-exchange between R3SiH/D and XSH/D and the thiol-catalysed racemisation of (S)-ButMePhSiH, radical-chain processes that provide independent confirmation of the values of kXSH derived from octyl bromide reduction. The value of ΔrH determined in this work indicates that abstraction of hydrogen from Et3SiH by an alkanethiyl radical in cyclohexane solvent is ca. 11 kJ mol-1 less endothermic than implied by the difference in the currently-favoured experimental gas-phase dissociation enthalpies for the Et3Si-H and MeS-H bonds.
- Cai, Yudong,Roberts, Brian P.
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p. 1858 - 1868
(2007/10/03)
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- Formation of silanethiols by reaction of silanes with carbonyl sulfide: Implications for radical-chain reduction of thiocarbonyl compounds by silanes
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Carbonyl sulfide reacts with organosilanes at 60-85°C, in the presence of a radical initiator, to give the corresponding silanethiols. Triphenylsilane is confirmed as an excellent replacement for tributyltin hydride in the Barton-McCombie deoxygenation of alcohols via thier xanthates under mild conditions. Reduction of xanthates by silanes can produce COS as a by-product, leading to the in situ formation of silanethiol that will then act as a protic polarity-reversal catalyst for the reduction.
- Cai, Yudong,Roberts, Brian P.
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p. 763 - 766
(2007/10/03)
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- THIOLS, UNSYMMETRICAL SULFIDES AND THIOACETALS FROM THE NEW REAGENT: TRIISOPROPYLSILANETHIOL
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Triisopropylsilanethiol (HSTIPS, 1), easily prepared in 98percent yield from H2S and TIPSCl, is efficiently alkylated in a selective manner with 10 and 20 alkyl halides or tosylates through its potassium thiolate (2c) to provide RSTIPS (3) in excellent yields.Compound 3 provides a convenient source of alkanethiols (4), unsymmetrical dialkyl sulfides (5) and thioacetals (6).
- Miranda, Edgar I.,Diaz, Michael J.,Rosado, Izander,Soderquist, John A.
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p. 3221 - 3224
(2007/10/02)
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