- A NEW METHOD FOR DEOXYGENATION OF VICINAL DIOLS
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Cis and trans vicinal diols have been converted into olefins in one step reaction with chlorotrimethylsilane and sodium iodide.
- Barua, Nabin C.,Sharma, Ram P.
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- New solid phase triorganogermanium hydrides for radical synthesis
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New solid phase triorganogermanium hydrides have been synthesized by the addition of a simple triorganogermanium hydride unit onto Quadragel and Merrifield resins. The new solid phase germanium hydrides have been used to mediate a range of synthetic radical reactions.
- Bowman, W. Russell,Krintel, Sussie L.,Schilling, Mark B.
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- Synthesis and biological studies of steroidal pyran based derivatives
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Steroid based cancer chemotherapeutic agents of the type 2′-amino-3′-cyanocholest-6-eno[5,7-de]4H-pyrans (1c-3c) have been synthesized and characterized by the various spectroscopic and analytical techniques. The DNA binding studies of compounds (1c-3c) with CT DNA were carried out by UV-vis and fluorescence spectroscopy and gel electrophoresis. The compounds (1c-3c) bind to DNA preferentially through electrostatic and hydrophobic interactions with Kb values found to be 5.4 × 103, 2.3 × 103 M-1 and 1.97 × 103 M-1, respectively indicating the higher binding affinity of compound (1c) towards DNA. The molecular docking study suggested that the electrostatic interaction of compounds (1c-3c) in between the nucleotide base pairs is due to the presence of pyran moiety in steroid molecule. All the compounds (1c-3c) cleave supercoiled pBR322 DNA via hydrolytic pathway, as validated by T4 DNA ligase assay. The compounds (1c-3c) were screened for in vitro cytotoxicity against the cancer and non-cancer cells SW480, A549, HepG2, HeLa, MCF-7, HL-60, DU-145, NL-20, HPC and HPLF by MTT assay. The compounds (1c-3c) were tested for genotoxicity (comet assay) involving apoptotic degradation of DNA and was analyzed by agarose gel electrophoresis and visualized by ethidium bromide staining. The results revealed that compound (1c) has better prospectus to act as cancer chemotherapeutic candidate which warrants further in vivo anticancer investigations.
- Shamsuzzaman,Dar, Ayaz Mahmood,Khan, Yusuf,Sohail, Aamir
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- Mild olefin formationviabio-inspired vitamin B12photocatalysis
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Dehydrohalogenation, or elimination of hydrogen-halide equivalents, remains one of the simplest methods for the installation of the biologically-important olefin functionality. However, this transformation often requires harsh, strongly-basic conditions, rare noble metals, or both, limiting its applicability in the synthesis of complex molecules. Nature has pursued a complementary approach in the novel vitamin B12-dependent photoreceptor CarH, where photolysis of a cobalt-carbon bond leads to selective olefin formation under mild, physiologically-relevant conditions. Herein we report a light-driven B12-based catalytic system that leverages this reactivity to convert alkyl electrophiles to olefins under incredibly mild conditions using only earth abundant elements. Further, this process exhibits a high level of regioselectivity, producing terminal olefins in moderate to excellent yield and exceptional selectivity. Finally, we are able to access a hitherto-unknown transformation, remote elimination, using two cobalt catalysts in tandem to produce subterminal olefins with excellent regioselectivity. Together, we show vitamin B12to be a powerful platform for developing mild olefin-forming reactions.
- Bam, Radha,Pollatos, Alexandros S.,Moser, Austin J.,West, Julian G.
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p. 1736 - 1744
(2021/02/22)
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- Red-light-mediated BartonMcCombie reaction
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A red-light-mediated BartonMcCombie reaction is described, in which chlorophyll a is used as a photocatalyst and tris(trimethylsilyl)silane or Hantzsch ester is used as the hydrogen source. The reaction can be performed with a set of easily available equipment and reagents, and a variety of linear and cyclic xanthates could be applied. In contrast to the traditional conditions, the reaction does not involve toxic organotin or an explosive radical initiator. The reaction mechanism was analyzed both by experiments and computation, and it was suggested that the radical chain mechanism initiated by excitation of complex followed by charge transfer is likely to be operative.
- Ichii, Naoki,Ogura, Akihiro,Shibata, Kouhei,Takao, Ken-Ichi
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supporting information
p. 936 - 941
(2020/11/09)
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- Iron-catalyzed protodehalogenation of alkyl and aryl halides using hydrosilanes
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A simple and efficient iron-catalyzed protodehalogenation of alkyl and aryl halides using phenylhydrosilane is disclosed. The reaction utilizes FeCl3 without the requirement of ligands. Unactivated alkyl and aryl halides were successfully reduced in good yields; sterically hindered tertiary halides were also reduced including the less reactive chlorides. The scalability of this methodology was demonstrated by a gram-scale synthesis with a catalyst loading as low as 0.5 mol%. Notably, disproportionation of phenylsilane leads to diphenylsilane that further reduces the halides. Preliminary mechanistic studies revealed a non-radical pathway and the source of hydrogen is PhSiH3via deuterium labeling studies. Our methodology represents simplicity and provides a good alternative to typical tin, aluminum and boron hydride reagents.
- Pilli, Ramadevi,Balakrishnan, Venkadesh,Chandrasekaran, Revathi,Rasappan, Ramesh
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supporting information
p. 1749 - 1753
(2019/02/20)
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- A Free-Radical Reduction and Cyclization of Alkyl Halides Mediated by FeCl2
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Iron mediated catalytic reactions are of great interest in the field of organic synthesis because they are economic and naturally abundant. However, the use of iron catalyst in the field of free radical cyclization or reduction of alkyl halides remains limited. Here we describe the use of an unprecedented combination of iron and zinc in the reduction and 5-exo-trig radical cyclization of alkyl halides under mild condition in the absence of added ligands or additives. The method is distinguished by its wide scope, functional group tolerance and the use of 1,4-cyclohexadiene as the source of hydrogen, which aids easy purification.
- Pulikottil, Feba Thomas,Pilli, Ramadevi,Murugesan, Vetrivelan,Krishnan, Chandu G.,Rasappan, Ramesh
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p. 2438 - 2442
(2019/04/30)
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- 4-Methyltetrahydropyran (4-MeTHP): Application as an Organic Reaction Solvent
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4-Methyltetrahydropyran (4-MeTHP) is a hydrophobic cyclic ether with potential for industrial applications. We herein report, for the first time, a comprehensive study on the performance of 4-MeTHP as an organic reaction solvent. Its broad application to organic reactions includes radical, Grignard, Wittig, organometallic, halogen-metal exchange, reduction, oxidation, epoxidation, amidation, esterification, metathesis, and other miscellaneous organic reactions. This breadth suggests 4-MeTHP can serve as a substitute for conventional ethers and harmful halogenated solvents. However, 4-MeTHP was found incompatible with strong Lewis acids, and the C?O bond was readily cleaved by treatment with BBr3. Moreover, the radical-based degradation pathways of 4-MeTHP, THP and 2-MeTHF were elucidated on the basis of GC-MS analyses. The data reported herein is anticipated to be useful for a broad range of synthetic chemists, especially industrial process chemists, when selecting the reaction solvent with green chemistry perspectives.
- Kobayashi, Shoji,Tamura, Tomoki,Yoshimoto, Saki,Kawakami, Takashi,Masuyama, Araki
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p. 3921 - 3937
(2019/11/11)
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- 1-Butyl-3-methylimidazol-2-ylidene Borane: A Readily Available, Liquid N-Heterocyclic Carbene Borane Reagent
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1-Butyl-3-methylimidazol-2-ylidene borane has been synthesized directly from two inexpensive commercial reagents: 1-butyl-3-methylimidazolium bromide and sodium borohydride. This NHC-borane reagent is a stable, free-flowing liquid that shows promise for use in radical, ionic, and metal-catalyzed reactions.
- Bolt, Daniel A.,Curran, Dennis P.
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p. 13746 - 13750
(2017/12/26)
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- Multiple Enone-Directed Reactivity Modes Lead to the Selective Photochemical Fluorination of Polycyclic Terpenoid Derivatives
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In the realm of aliphatic fluorination, the problem of reactivity has been very successfully addressed in recent years. In contrast, the associated problem of selectivity, that is, directing fluorination to specific sites in complex molecules, remains a great, fundamental challenge. In this report, we show that the enone functional group, upon photoexcitation, provides a solution. Based solely on orientation of the oxygen atom, site-selective photochemical fluorination is achieved on steroids and bioactive polycycles with up to 65 different sp3 C-H bonds. We have also found that γ-, β-, homoallylic, and allylic fluorination are all possible and predictable through the theoretical modes reported herein. Lastly, we present a preliminary mechanistic hypothesis characterized by intramolecular hydrogen atom transfer, radical fluorination, and ultimate restoration of the enone. In all, these results provide a leap forward in the design of selective fluorination of complex substrates that should be relevant to drug discovery, where fluorine plays a prominent role.
- Pitts, Cody Ross,Bume, Desta Doro,Harry, Stefan Andrew,Siegler, Maxime A.,Lectka, Thomas
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supporting information
p. 2208 - 2211
(2017/02/23)
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- Catechols as Sources of Hydrogen Atoms in Radical Deiodination and Related Reactions
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When used with trialkylboranes, catechol derivatives, which are low-cost and low toxicity, are valuable hydrogen atom donors for radical chain reactions involving alkyl iodides and related radical precursors. The system 4-tert-butylcatechol/triethylborane has been used to reduce a series of secondary and tertiary iodides, a xanthate, and a thiohydroxamate ester. Catechol derivatives are right in the optimal kinetic window for synthetic applications, as demonstrated by highly efficient radical cyclizations. Cyclizations leading to the formation of quaternary centers can be performed in an all-at-once process (no slow addition of the hydrogen atom donor) at standard concentrations. The H-donor properties of catechol derivatives can be fine-tuned by changing their substitution pattern. In slow radical cyclization processes, an enhanced ratio of cyclized/uncyclized products was obtained by using 3-methoxycatechol instead of 4-tert-butylcatechol.
- Povie, Guillaume,Ford, Leigh,Pozzi, Davide,Soulard, Valentin,Villa, Giorgio,Renaud, Philippe
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supporting information
p. 11221 - 11225
(2016/10/13)
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- The Use of Ureates as Activators for Samarium Diiodide
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A novel mode of SmI2 activation has been developed using ureates as reaction promoters. Several ureates formed by treatment of the corresponding ureas with n-BuLi have been shown to activate SmI2 to a substantial extent toward the reduction of 1-chlorodecane. Complexes formed from SmI2 and various ureates have been shown to be useful for the reduction of a variety of organohalides, including substrates of low reactivity such as aryl fluorides. Because of ease of synthesis and low molecular weight, the conjugate base of triethylurea (TEU-) was of primary focus. Visible spectroscopy and reactivity data are consistent with the hypothesis that the same complex is being formed when SmI2 is combined with either 2 or 4 equiv of TEU-, in spite of the greater reactivity of SmI2/4 TEU- with some alkyl halides. We propose that the active reductant is an N,O chelate formed between SmI2 and 2 equiv of TEU-.
- McDonald, Chriss E.,Ramsey, Jeremy D.,McAtee, Christopher C.,Mauck, Joseph R.,Hale, Erin M.,Cumens, Justin A.
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p. 5903 - 5914
(2016/07/23)
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- Synthesis and characterization of steroidal heterocyclic compounds, DNA condensation and molecular docking studies and their in vitro anticancer and acetylcholinesterase inhibition activities
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A facile, convenient and efficient approach for the synthesis of a new series of steroidal heterocyclic compounds (4-12) by reacting a mixture of compounds (1e-3e) with o-aminothiophenol/o-aminophenol/o-phenylenediamine is reported. The structural assignment of products is confirmed on the basis of IR, 1H NMR, 13C NMR, MS and analytical data. The compounds obey the Lipinski's 'Rule of Five' analysis based on computational prediction and pharmacokinetic properties. The anticancer activity has been tested in vitro against three cancer cell lines Hep3B (human hepatocellular carcinoma), MCF7 (human breast adenocarcinoma), HeLa (human cervical carcinoma) and one non-cancer normal cell i.e. PBMCs (peripheral blood mononuclear cell) by MTT assay. In addition, the synthesized compounds are also tested for their in vitro antioxidant activity by various reported methods in which compounds 10-12 exhibited good antioxidant activity. Nonenzymatic degradation of DNA has been investigated. The acetylcholinesterase (AChE) inhibitor activities of the steroidal derivatives are also evaluated using Ellman's method. Moreover, the application of compound 6 as a DNA gene transporter is evaluated by DNA condensation and ascertained by employing TEM and AFM, which illustrate that the compound 6 induces the condensation of CT-DNA. Molecular docking studies further characterize the interaction of the synthesized compounds with DNA. 2015
- Ali, Abad,Asif, Mohd,Khanam, Hena,Mashrai, Ashraf,Sherwani, Mohd Asif,Owais, Mohammad,Shamsuzzaman
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p. 75964 - 75984
(2015/09/28)
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- Scope and Mechanistic Analysis for Chemoselective Hydrogenolysis of Carbonyl Compounds Catalyzed by a Cationic Ruthenium Hydride Complex with a Tunable Phenol Ligand
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A cationic ruthenium hydride complex, [(C6H6)(PCy3)(CO)RuH]+BF4- (1), with a phenol ligand was found to exhibit high catalytic activity for the hydrogenolysis of carbonyl compounds to yield the corresponding aliphatic products. The catalytic method showed exceptionally high chemoselectivity toward the carbonyl reduction over alkene hydrogenation. Kinetic and spectroscopic studies revealed a strong electronic influence of the phenol ligand on the catalyst activity. The Hammett plot of the hydrogenolysis of 4-methoxyacetophenone displayed two opposite linear slopes for the catalytic system 1/p-X-C6H4OH (ρ = -3.3 for X = OMe, t-Bu, Et, and Me; ρ = +1.5 for X = F, Cl, and CF3). A normal deuterium isotope effect was observed for the hydrogenolysis reaction catalyzed by 1/p-X-C6H4OH with an electron-releasing group (kH/kD = 1.7-2.5; X = OMe, Et), whereas an inverse isotope effect was measured for 1/p-X-C6H4OH with an electron-withdrawing group (kH/kD = 0.6-0.7; X = Cl, CF3). The empirical rate law was determined from the hydrogenolysis of 4-methoxyacetophenone: rate = kobsd[Ru][ketone][H2]-1 for the reaction catalyzed by 1/p-OMe-C6H4OH, and rate = kobsd[Ru][ketone][H2]0 for the reaction catalyzed by 1/p-CF3-C6H4OH. Catalytically relevant dinuclear ruthenium hydride and hydroxo complexes were synthesized, and their structures were established by X-ray crystallography. Two distinct mechanistic pathways are presented for the hydrogenolysis reaction on the basis of these kinetic and spectroscopic data. (Chemical Equation Presented).
- Kalutharage, Nishantha,Yi, Chae S.
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supporting information
p. 11105 - 11114
(2015/09/15)
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- Molybdenum-mediated desulfurization of dhiols and disulfides
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We have successfully achieved the molybdenum hexacarbonyl [Mo(CO) 6] mediated desulfurization of thiols and disulfides. In this reaction, the sulfhydryl (SH) mercapto groups of aryl, benzyl, primary and secondary alkyl thiols, and S-S single bonds of disulfides can be removed. This reaction has high functional group tolerance and is not affected by steric hindrance. The results of the reactions in acetone-d 6 suggest that the sources of hydrogen in the thiol and disulfide desulfurizations are the hydrogen atom(s) of a sulfhydryl group and acetone (solvent), respectively, and that the desulfurization proceeds via the formation of an organomolybdenum species. Georg Thieme Verlag Stuttgart. New York.
- Wang, Zhen,Kuninobu, Yoichiro,Kanai, Motomu
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supporting information
p. 1869 - 1872
(2014/08/18)
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- Aqueous reduction of iodosteroids to deoxysteroids
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A new method for the reduction of iodosteroids to deoxysteroids has been developed using Zn, HCOOH and a catalytic amount of Aliquat 336 in water. In total, 13 iodosteroids were reduced in good to excellent yields. The higher solubilities of the substrates lead to the faster reactions, and the aqueous reaction was efficiently accelerated by granular polytetrafluoroethylene. The advantage of the aqueous system over eight organic solvents has also been demonstrated.
- Liu, Changsheng,Sun, Lili,Li, Chunbao
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p. 309 - 312
(2014/06/09)
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- Selective reduction of α,β-unsaturated steroidal carbonyl compounds by NaBH4in presence of guanidine hydrochloride in dioxane
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A selective hydrogenation of α,β-unsaturated steroidal carbonyl compounds with NaBH4in the presence of guanidine hydrochloride in dioxane in good to excellent yields are described.
- Khan, Salman Ahmad,Asiri, Abdullah M.
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p. 6331 - 6334
(2015/02/19)
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- Evaluation of cyclopentyl methyl ether (CPME) as a solvent for radical reactions
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We have explored the potential of cyclopentyl methyl ether (CPME) as a solvent for radical reactions. Hydrostannation, hydrosilylation, hydrothiolation, and tributyltin hydride mediated reductions were successfully carried out in CPME. GC-MS analysis indicated that CPME degraded into methyl pentanoate, cyclopentanone, 2-cyclopenten-1-ol, and cyclopentanol under thermal radical conditions, albeit only slightly. We also achieved radical-containing one-pot reactions in CPME as a demonstration of its applicability to multi-step reactions.
- Kobayashi, Shoji,Kuroda, Hiroyuki,Ohtsuka, Yuta,Kashihara, Takashi,Masuyama, Araki,Watanabe, Kiyoshi
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p. 2251 - 2259
(2013/03/29)
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- Batch to flow deoxygenation using visible light photoredox catalysis
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Herein we report a one-pot deoxygenation protocol for primary and secondary alcohols developed via the combination of the Garegg-Samuelsson reaction, visible light-photoredox catalysis, and flow chemistry. This procedure is characterized by mild reaction conditions, easy-to-handle reactants and reagents, excellent functional group tolerance, and good yields.
- Nguyen, John D.,Reiss, Barbara,Dai, Chunhui,Stephenson, Corey R. J.
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supporting information
p. 4352 - 4354
(2013/06/05)
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- Radical-mediated reduction of the dithiocarbamate group under tin-free conditions
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Reductive desulfurisation of dithiocarbamates is conveniently achieved using H3PO2-Et3N-ACCN in refluxing dioxane. Fused and spirocyclic β-lactams, prepared through 4-exo trig carbamoyl radical cyclisation-dithiocarbamate group transfer reactions, are reduced without fragmentation of the strained 4-membered ring. Diethyl tetraacetyl-d-glucopyranosyl dithiocarbamate is selectively reduced with or without acyloxy group migration depending on reaction conditions and choice of reductant. Deuterium incorporation from D3PO2-Et 3N is observed for a system involving a nucleophilic radical intermediate, but not in the case of the electrophilic radical obtained through acyloxy group migration on a glucose derivative.
- McMaster, Claire,Bream, Robert N.,Grainger, Richard S.
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experimental part
p. 4752 - 4758
(2012/08/08)
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- Polarity reversal catalysis in radical reductions of halides by N-heterocyclic carbene boranes
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Otherwise sluggish or completely ineffective radical reductions of alkyl and aryl halides by N-heterocyclic carbene boranes (NHC-boranes) are catalyzed by thiols. Reductions and reductive cyclizations with readily available 1,3-dimethylimidazol-2-ylidene borane and a water-soluble triazole relative are catalyzed by thiophenol and tert-dodecanethiol [C9H 19C(CH3)2SH]. Rate constants for reaction of the phenylthiyl (PhS?) radical with two NHC-boranes have been measured to be ~108 M-1 s-1 by laser flash photolysis experiments. An analysis of the available evidence suggests the operation of polarity reversal catalysis.
- Pan, Xiangcheng,Lacote, Emmanuel,Lalevee, Jacques,Curran, Dennis P.
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supporting information; experimental part
p. 5669 - 5674
(2012/06/04)
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- Synthesis and biological evaluation of some thiazolidinone derivatives of steroid as antibacterial agents
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Steroidal thiazolidinone derivatives were prepared by the multi-step reactions of steroid. It is prepared from steroidal thiosemicarbazones with ethyl bromoacetate in dioxane. Steroidal thiosemicarbazones were prepared by the reaction of thiosemicarbazide with steroidal ketones. The structures of these compounds were elucidated by IR, 1H NMR, Fab mass spectrometries and their purities were confirmed by elemental analyses. The antibacterial activity of these compounds was evaluated by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria and then the minimum inhibitory concentration (MIC) of compounds was determined. The results showed that steroidal thiazolidinone derivatives are better in inhibiting the growth as compared to steroidal thiosemicarbazone derivatives of both types of the bacteria (Gram-positive and Gram-negative). Compounds 7 and 8 are better antibacterial agents as compared to standard drug Amoxicillin.
- Khan, Salman Ahmad,Yusuf, Mohammed
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scheme or table
p. 2597 - 2600
(2009/10/09)
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- Radical chain reactions using THP as a solvent
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THP (tetrahydropyran) has been found to show an excellent stability towards autooxidation, compared with THF. Tributyltin hydride mediated radical cyclization, when conducted in THF as a solvent, suffers from competition of hydrogen abstraction from the solvent, whereas the use of THP resulted in the course to negligible degree. Tributyltin hydride, TTMSS, and hexanethiol mediated radical reactions were carried out successfully using THP as a solvent.
- Yasuda, Hiroshi,Uenoyama, Yoshitaka,Nobuta, Osamu,Kobayashi, Shoji,Ryu, Ilhyong
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p. 367 - 370
(2008/09/17)
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- Synthesis and in vitro antibacterial activity of new steroidal thiosemicarbazone derivatives
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We investigated the antibacterial activity of some new steroidal thiosemicarbazone derivatives, prepared from the reaction of cholest-5-en-7-one with thiosemicarbazides, in ethanol in the presence of a few drops of HCl at 80 °C in high yield. All the compounds have been characterized by means of elemental analyses, IR, 1H NMR and mass spectroscopic data, to find an effective antibacterial agent. The antibacterial activity was first tested in vitro by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria, and then the minimum inhibitory concentration (MIC) of compounds was determined. The results showed that the steroidal thiosemicarbazones derivatives inhibit growth of both types of the bacteria (Gram-positive and Gram-negative). The acetoxy and chloro derivatives of cyclopentyl and cyclohexyl amine thiosemicarbazones were found to have more antibacterial activity than the other derivatives.
- Khan, Salman Ahmad,Kumar, Praveen,Joshi, Rajkumar,Iqbal, Prince F.,Saleem, Kishwar
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p. 2029 - 2034
(2008/12/22)
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- On the scope of radical reactions in aqueous media utilizing quaternary ammonium salts of phosphinic acids as chiral and achiral hydrogen donors
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A broad range of fundamental free radical reactions such as hydrogen atom transfer, radical deoxygenations, and radical cyclizations utilizing quaternary ammonium salts of phosphinic acids as chiral and achiral hydrogen donors at room temperature are investigated. The reactions proceed in good to excellent yields with some degree of enantioselectivity.
- Perchyonok,Tuck, Kellie L.,Langford, Steven J.,Hearn, Milton W.
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p. 4777 - 4779
(2008/12/22)
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- Deoxygenation of alcohols employing water as the hydrogen atom source
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Trialkylboranes (BMe3, BEt3, and BBu3) have been shown to mediate reductive deoxygenation reactions of O-alkyl-S-methyl dithiocarbonates (methyl xanthates) in which water or deuterium oxide functions as the source of hydrogen or deuterium. This method has proven versatile with regard to substrate scope and is capable of providing protio- or deuterioalkane products in high yields with excellent levels of D-incorporation. Ab initio calculations suggest that the trialkylborane-water complex possesses an unusually low O-H bond dissociation energy (73 kcal/mol) and support a radical chain mechanism for this process. Taken together, this report provides evidence for fundamentally novel and previously overlooked modes of reactivity for water and trialkylboranes of wide ranging importance in both theoretical and applied investigations. Copyright
- Spiegel, David A.,Wiberg, Kenneth B.,Schacherer, Laura N.,Medeiros, Matthew R.,Wood, John L.
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p. 12513 - 12515
(2007/10/03)
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- Tributylgermanium hydride as a replacement for tributyltin hydride in radical reactions
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Tributylgermanium hydride (Bu3GeH) can be used as an alternative to tributyltin hydride (Bu3SnH) as a radical generating reagent with a wide range of radical substrates. Tributylgermanium hydride has several practical advantages over tributyltin hydride, e.g. low toxicity, good stability and much easier work-up of reactions. The reagent can be easily prepared in good yield and stored indefinitely. Suitable substrates include iodides, bromides, activated chlorides, phenyl selenides, tert-nitroalkanes, thiocarbonylimidazolides and Barton esters. Alkyl, vinyl and aryl radicals can be generated in radical reactions including reduction and cyclisation processes. Common radical initiators such as ACCN and triethylborane can be used. The slower rate of hydrogen abstraction by carbon-centred radicals from Bu 3GeH as compared to Bu3SnH facilitates improved cyclisation yields. Polarity reversal catalysis (PRC) with phenylthiol can be used in reactions which generate stable radical intermediates which will not abstract hydrogen from Bu3GeH.
- Bowman, W. Russell,Krintel, Sussie L.,Schilling, Mark B.
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p. 585 - 592
(2007/10/03)
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- Rapid defunctionalization of carbonyl group to methylene with polymethylhydrosiloxane-B(C6F5)3
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The polymethylhydrosiloxane-B(C6F5)3 combination is found to be a versatile carbonyl defunctionalization system under mild and rapid conditions. For the first time, B(C6F5)3 has been used as a nonconventional Lewis acid catalyst to activate PMHS. Aromatic and aliphatic carbonyl compounds were effectively reduced to give the corresponding alkanes in high yields.
- Chandrasekhar,Raji Reddy, Ch.,Nagendra Babu
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p. 9080 - 9082
(2007/10/03)
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- Radical deoxygenation of alcohols and vicinal diols with N-ethylpiperidine hypophosphite in water
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Radical deoxygenation of alcohols and vicinal diols with N-ethylpiperidine hypophosphite both in alcohols and in water is described. S-Methyl dithiocarbonate and bis-S-methyl dithiocarbonate of carbohydrates and nucleosides were deoxygenated efficiently under reaction conditions.
- Jang, Doo Ok,Cho, Dae Hyan
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p. 5921 - 5924
(2007/10/03)
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- Preparation of steroid olefins from heptafluorobutyrates
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Steroids with hydroxyl group in positions 2, 3, 6, 7, 17 and 20 were esterified with heptafluorobutyric anhydride. The obtained esters on treatment with lithium bromide in N,N-dimethylacetamide in the presence of pyridinium tosylate afforded the corresponding olefins in high yields.
- Dalibov, Lucie,Kohout, Ladislav
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p. 549 - 556
(2007/10/03)
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- Reductive cleavage of N,N,N',N'-tetramethylphosphorodiamidate with lithium naphthalenide. A convenient procedure for deoxygenation of alcohols
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A simple, effective alternative procedure has been developed for the reductive cleavage of the N,N,N,'N'-tetramethylphosphorodiamidate group, using lithium naphthalenide as the reagent.
- Liu, Hsing-Jang,Shang, Xiao
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p. 367 - 370
(2007/10/03)
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- Novel enhancement of the reducing ability of ytterbium diiodide by irradiation with near-UV light
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Irradiation with near-UV light dramatically enhances the reducing ability of ytterbium diiodide (Ybl2). Organic bromides, iodides, tosylates, and tellurides are reduced efficiently by a YbI2-hv system, while these can not be reduced with YbI2 in the dark.
- Ogawa, Akiya,Ohya, Syoji,Sumino, Yukihito,Sonoda, Noboru,Hirao, Toshikazu
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p. 9017 - 9018
(2007/10/03)
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- Conversion of Thionoesters and Thionolactones to Ethers; a General and Efficient Radical Desulfurisation
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Triphenyltin hydride reduces thionoesters and thionolactones to their corresponding ethers in high yield.
- Nicolaou, Kyriacos C.,Sato, Mitsunobu,Theodorakis, Emmanuel A.,Miller, Neil D.
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p. 1583 - 1586
(2007/10/02)
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- Deoxygenation of aliphatic alcohols via reduction of new thioxocarbamate derivatives
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N-Acylthioxocarbamates, obtained by the reaction of alcohols with acyl isothiocyanates, were reduced by tributylstannane or triphenylsilane under radical conditions to give deoxygenated products of the corresponding alcohols in good yields. An application to regioselective deuteration using tributyldeuteriostannane is also examined.
- Oba,Nishiyama
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p. 624 - 628
(2007/10/02)
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- Addition reaction and deoxygenation of alcohols using isothiocyanates and triethylsilane-DTBP
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Alcohols were found to be deoxygenated through treatment with isothiocyanates giving thionocarbamates, followed by reduction with triethylsilane.
- Nishiyama,Oba,Oshimi,Sugawara,Ueno
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p. 3745 - 3748
(2007/10/02)
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- An Internally Activated Tin Hydride with Enhanced Reducing Ability
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Tin hydride 1 is activated for nucleophilic hydride transfer and also for radical chain reduction, depending on solvent.The nucleophilic hydride pathway is favored in methanol, and 1 can be used as a selective reducing agent for ketones.Simple ketones are not reduced in aprotic solvents, but β-hydroxy ketones are activated internally by the hydroxyl group and can be reduced in THF with good control of stereochemistry, as in the conversion from 7 to 9 (30:1 9:8).A catalytic version of the nucleophilic hydride reductions in methanol has been developed using PhSiH3 as the stoichiometric hydride source.Radical chain dehalogenations can also be achieved with 1 at room temperature and without added radical initiators.Simple xanthates are not reduced efficiently in the absence of an initiator, but the reaction proceeds in the presence of AIBN.
- Vedejs, E.,Duncan, S. M.,Haight, A. R.
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p. 3046 - 3050
(2007/10/02)
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- A Facile Method for the Reductive Deoxygenation of Aliphatic Oxygen-Functionalized Compounds
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A one-pot three-step sequence for the reductive removal of oxygen from aliphatic carboxylic acids, ketones, aldehydes and alcohols to yield alkanes or alkyl groups has been developed.This was achieved by reducing the substrates to the alcohol level with lithium aluminium hydride followed by in situ preparation of the corresponding alkyl sulfate which is finally treated with a second portion of lithium aluminium hydride.Yields as determined by gas liquid chromatography were in the range 89-99percent.Preparative experiments with 1-decanol and decanoic acid afforded 92 and 81percent yield, respectively, of distilled decane.The effect of various additives on the yield of the reaction is reported.Improvement of a recently reported method for the conversion of 1,4a-dimethyl-1α,8aα-epoxyperhydronaphthalen-2-one into r-1,t-4a-dimethylperhydronaphthalen-c-8a-ol and some observations concerning the reduction of cholesterol are also discussed.
- Hansson, Lars,Carlson, Rolf
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p. 103 - 107
(2007/10/02)
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- Radical Chain Reduction of Alkyl Halides, Dialkyl Sulphides and O-Alkyl S-Methyl Dithiocarbonates to Alkanes by Trialkylsilanes
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Saturated primary, secondary and tertiary alkyl halides RX (X = Cl, Br or I) are reduced to the corresponding alkanes RH in essentially quantitative yield by triethylsilane in refluxing hexane or cyclohexane in the presence of a suitable initiator and an alkanethiol catalyst.Reduction proceeds by a radical chain mechanism and the thiol acts as a polarity reversal catalyst which mediates hydrogen-atom transfer from the Si-H group of the silane to the alkyl radical R..Triphenylsilanethiol and perfluorohexanesulphenyl chloride are also effective catalysts; the latter is probably reduced in situ to the corresponding fluorinated thiol.Other silanes R3SiH (R = Prn, Pri or Ph) also bring about reduction.The silane-thiol couple therefore serves as a useful replacement for tributylstannane as a homolytic reducing agent for alkyl halides.Reduction of 6-bromohex-1-ene, to give a mixture of hex-1-ene and methylcyclopentane, is more sluggush than reduction of saturated halides and this is attributed to removal of the thiol catalyst by addition across the C=C bond.Ethyl 4-bromobutanoate is smoothly reduced to ethyl butanoate without interference from the ester function.Dialkyl sulphides are reduced to alkanes by triethylsilane in a radical chain reaction, but the effect of added thiol depends on the nature of the S-alkyl groups in the sulphide.The trialkylsilane-thiol couple can also successfully replace trialkylstannane as the reducing agent in the Barton-McCombie deoxygenation of primary and secondary alcohols via their S-methyl dithiocarbonate (xanthate) esters.Good yields of deoxy compounds are obtained from octan-1-ol, octan-2-ol, octadecan-1-ol, 5α-cholestan-3β-ol, cholesterol and 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose.
- Cole, Stephen J.,Kirwan, J. Nicholas,Roberts, Brian P.,Willis, Colin R.
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p. 103 - 112
(2007/10/02)
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- A Polymer-Supported Organotin Hydride and Its Multipurpose Application in Radical Organic Synthesis
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The multipurpose application of a polystyrene-supported, regenerable organotin hydride for radical organic syntheses is demonstrated using 10 examples taken from dehalogenation of bulky or multifunctional halides, dehydroxylation of secondary alcohols, and deamination of secondary or tertiary amines.
- Gerlach, Martin,Joerdens, Frank,Kuhn, Heiko,Neumann, Wilhelm P.,Peterseim, Markus
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p. 5971 - 5972
(2007/10/02)
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- REGIOSELECTIVE TRANSFORMATION OF ALLYLIC, BENZYLIC AND TERTIARY ALCOHOLS INTO THE CORRESPONDING IODIDES WITH ALUMINIUM TRIIODIDE : DEOXYGENATION OF VICINAL DIOLS
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Aluminium triiodide regioselectively converts allylic, benzylic and tertiary alcohols into the corresponding iodides in excellent yields.It also deoxygenates cis and trans secondary-tertiary and allylic bis-secondary vicinal diols in good yields.
- Sarmah, Parijat,Barua, Nabin C
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p. 3569 - 3574
(2007/10/02)
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- ALUMINIUM TRIIODIDE: A CONVENIENT REAGENT FOR DEOXYGENATION OF OXIRANES
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Freshly prepared Aluminium triiodide has been shown to deoxygenate a variety of oxiranes to the corresponding olefins in excellent yields.In case of less reactive oxiranes such as entry 6, 7, 8 and 9 the initial formation of the trans-iodohydrins was observed.
- Sarmah, Parijat,Barua, Nabin C
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p. 5815 - 5816
(2007/10/02)
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- p-Bis(diphenylhydrosilyl)benzene. A useful Reagent for the Deoxygenation of Alcohols via Acetates
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Acetates which were derived from primary, secondary, and tertiary alcohols were deoxygenated to the corresponding hydrocarbons in high yield by p-bis(diphenylhydrosilyl)benzene under homolytic conditions.
- Sano, Hiroshi,Takeda, Toshimitsu,Migita, Toshihiko
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p. 119 - 122
(2007/10/02)
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- Thermolytic Transformation of Steroidal Nitroimines
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Thermolysis of 6-nitroimino-5α-cholestan-3β-yl acetate (I), 6-nitroimino-5α-cholestane (VII) and 7-nitroiminocholest-5-en-3β-yl chloride (XII) in refluxing xylene affords a mixture of products in the case of I and VII and a chlorine-free product in the case of XII.The known products have been characterized by direct comparison while unknown products by elemental analyses and spectral data.
- Ahmad, M. S.,Raza, S. K.
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p. 259 - 260
(2007/10/02)
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- A simple Method for the Transformation of Steroidal Epoxides to Olefins
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5,6α-Oxido-5α-cholestane (1) and its 3β-substituted analogues (2-4) on silver nitrate-neutral alumina surface were readily converted to cholest-5-ene (5) and its 3β-substituted analogues (6-8) in 90-95percent yield.
- Shafiullah,Pathak, R. K.
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p. 668 - 669
(2007/10/02)
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- A Mild and Convenient Method for the Reduction of Organic Halides by Using a SmI2-THF Solution in the Presence of Hexamethylphosphoric Triamide (HMPA)
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A remarkable effect of HMPA was observed in the reduction of organic halides with a SmI2-THF solution.Various types of organic halides were reduced rapidly to the corresponding alkanes in almost quantitative under mild reaction conditions.
- Inanaga, Junji,Ishikawa, Mitsuhiro,Yamaguchi, Masaru
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p. 1485 - 1486
(2007/10/02)
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- TRIS(3,6-DIOXAHEPTYL)AMINE: A SUPERIOR COMPLEXING AGENT FOR DISSOLVING METAL REACTIONS
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Commercially available tris(3,6-dioxaheptyl)amine (TDA-1) is an effective phase transfer catalyst for reactions with sodium-potassium alloy in tetrahydrofuran.Deoxygenation of acetates, dehalogenation, and hydrolysis of tosylates and mesylates proceed in high yield.The use of a deuterated alcohol during deoxygenation reactions leads to site-specific deuteration.
- Bose, Ajay K.,Mangiaracina, Pietro
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p. 2503 - 2506
(2007/10/02)
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- A RADICAL DEOXIGENATION OF SECONDARY ALCOHOLS TO HYDROCARBONS BY USE OF TRIBUTYLTIN HYDRIDE
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Secondary alcohols 1 reacted with 2,2'-dibenzothiazolyldisulfide in the presence of tributylphosphine to give corresponding sulfides 2 in good yields.Sulfides 2 were subsequently desulfurized to hydrocarbons 3 with tributyltin hydride in radical conditions.
- Watanabe, Yoshihiko,Araki, Takumi,Ueno, Yoshio,Endo, Takeshi
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p. 5385 - 5388
(2007/10/02)
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- 1,1'-Thiocarbonyldi-2,2'-pyridone. A New Useful Reagent for Functional Group Conversions under Essentially Neutral Conditions
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1,1'-Thiocarbonyldi-2,2'-pyridone is a useful reagent for the preparation of nitriles, carbodiimides, cyclic thionocarbonates, and isothiocyanates and deoxygenation of alcohols under essentially neutral conditions.
- Kim, Sunggak,Yi, Kyu Yang
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p. 2613 - 2615
(2007/10/02)
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- The Invention of New Radical Chain Reactions. Part 11. A New Method for the Generation of Tertiary Radicals from Tertiary Alcohols
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A convenient procedure for the radical deoxygenation of tertiary alcohols has been invented using the double half esters of oxalic acid with the t-alcohol and N-hydroxypyridine-2-thione.Decomposition of this type of ester in the presence of 1,1-dimethylethane- or (better) 1,1-diethylpropane-thiol gave the corresponding hydrocarbons in good yield.It has been shown that the oxalate fragmentation is not concerted, but involves a stepwise loss of carbon dioxide.Tertiary alcohols are also a convenient source of radicals for addition to siutable alkenes with formation of quaternary centres.
- Barton, Derek H. R.,Crich, David
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p. 1603 - 1612
(2007/10/02)
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