- Reactivity of bismuth(III) halides towards alcohols. A tentative to mechanistic investigation
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The reactivity of bismuth(III) halides (BiX3; X=Cl, Br and I) towards a series of alcohols has been investigated. Three different reactions have been studied, namely: halogenation, dehydration and etherification. The behaviour of these bismuth derivatives was found to depend on the nature of the halide bonded to the bismuth atom. Their reactivities can be interpreted on the basis of the Hard and Soft Acids and Bases (HSAB) principle. A mechanism is proposed which involves the formation of a complex of the alcohol with Bi(III).
- Keramane, El Mehdi,Boyer, Bernard,Roque, Jean-Pierre
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- Site-Selective Aliphatic C-H Chlorination Using N-Chloroamides Enables a Synthesis of Chlorolissoclimide
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Methods for the practical, intermolecular functionalization of aliphatic C-H bonds remain a paramount goal of organic synthesis. Free radical alkane chlorination is an important industrial process for the production of small molecule chloroalkanes from simple hydrocarbons, yet applications to fine chemical synthesis are rare. Herein, we report a site-selective chlorination of aliphatic C-H bonds using readily available N-chloroamides and apply this transformation to a synthesis of chlorolissoclimide, a potently cytotoxic labdane diterpenoid. These reactions deliver alkyl chlorides in useful chemical yields with substrate as the limiting reagent. Notably, this approach tolerates substrate unsaturation that normally poses major challenges in chemoselective, aliphatic C-H functionalization. The sterically and electronically dictated site selectivities of the C-H chlorination are among the most selective alkane functionalizations known, providing a unique tool for chemical synthesis. The short synthesis of chlorolissoclimide features a high yielding, gram-scale radical C-H chlorination of sclareolide and a three-step/two-pot process for the introduction of the β-hydroxysuccinimide that is salient to all the lissoclimides and haterumaimides. Preliminary assays indicate that chlorolissoclimide and analogues are moderately active against aggressive melanoma and prostate cancer cell lines.
- Quinn, Ryan K.,K?nst, Zef A.,Michalak, Sharon E.,Schmidt, Yvonne,Szklarski, Anne R.,Flores, Alex R.,Nam, Sangkil,Horne, David A.,Vanderwal, Christopher D.,Alexanian, Erik J.
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supporting information
p. 696 - 702
(2016/02/03)
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- Stereoretentive chlorination of cyclic alcohols catalyzed by titanium(IV) tetrachloride: Evidence for a front side attack mechanism
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A mild chlorination reaction of alcohols was developed using the classical thionyl chloride reagent but with added catalytic titanium(IV) chloride. These reactions proceeded rapidly to afford chlorination products in excellent yields and with preference for retention of configuration. Stereoselectivities were high for a variety of chiral cyclic secondary substrates including sterically hindered systems. Chlorosulfites were first generated in situ and converted to alkyl chlorides by the action of titanium tetrachloride which is thought to chelate the chlorosulfite leaving group and deliver the halogen nucleophile from the front face. To better understand this novel reaction pathway, an ab initio study was undertaken at the DFT level of theory using two different computational approaches. This computational evidence suggests that while the reaction proceeds through a carbocation intermediate, this charged species likely retains pyramidal geometry existing as a conformational isomer stabilized through hyperconjugation (hyperconjomers). These carbocations are then essentially "frozen" in their original configurations at the time of nucleophilic capture.
- Mondal, Deboprosad,Li, Song Ye,Bellucci, Luca,Laino, Teodoro,Tafi, Andrea,Guccione, Salvatore,Lepore, Salvatore D.
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p. 2118 - 2127
(2013/04/10)
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- Regioselective Hydrochlorination of Olefins Is Favored by an Acidic Solid Catalyst
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With thionyl chloride SOCl2 as HCl precursor, 1-methylcyclohexene is hydrochlorinated.In the absence of a solid catalyst, between half and two-thirds of the product mixture are the anti-Markovnikov adduct, trans-1-chloro-2-methylcyclohexane.Catalysis by the ZF 520 zeolite or the K 10 montmorillonite makes the reaction selective.It then affords a quantitative yield of (10:1) Markovnikov adduct 1-chloro-1-methylcyclohexane. Key Words: Markovnikov; Anti-Markovnikov; Ionic; Radical; High Yield and Selectivity
- Delaude, Lionel,Laszlo, Pierre
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p. 3705 - 3708
(2007/10/02)
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- The Interaction of Arenesulphonyl Chlorides, Aluminium Chloride, and Saturated Alicyclic Hydrocarbons containing at least One Tertiary Hydrogen Atom
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Cycloalkanes having at least one tertiary hydrogen react with a mixture of benzenesulphonyl chloride and aluminium chloride in carbon disulphide, with reactivity decreasing in the order cis-decalin ca. cis-hexahydroindane > trans-decalin >/= dicyclohexyl > methylcyclohexane > t-butylcyclohexane > methylcyclopentane.Although hydrogen chloride was evolved and benzenesulphonyl chloride was reduced to benzenesulphinic acid in all the reactions, only cis-decalin, and, to a much smaller extent, dicyclohexyl, gave appreciable amounts of chloro- or dichloro-cycloalkanes.In other reactions the major products were hydrocarbon "dimers" and "trimers" apparently formed by attack by the carbenium ion on cycloalkenes formed in the reaction.Electron-attracting substituents in the arenesulphonyl chloride enhanced the rate of reaction with cis-decalin, and electron-donor substituents retarded the reaction, which appears to proceed via hydride-ion abstraction by the arenesulphonyl halide-aluminium halide "oxonium complex" rather than by the (+) ion.
- Ewedemi, Rotimi O.,Fields, Roy,Holt, Geoffrey
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p. 1466 - 1500
(2007/10/02)
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