- N -Hydroxyphthalimide/benzoquinone-catalyzed chlorination of hydrocarbon C-H bond using N -chlorosuccinimide
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The direct chlorination of C-H bonds has received considerable attention in recent years. In this work, a metal-free protocol for hydrocarbon C-H bond chlorination with commercially available N-chlorosuccinimide (NCS) catalyzed by N-hydroxyphthalimide (NHPI) with 2,3-dicyano-5,6-dichlorobenzoquinone (DDQ) functioning as an external radical initiator is presented. Aliphatic and benzylic substituents and also heteroaromatic ones were found to be well tolerated. Both the experiments and theoretical analysis indicate that the reaction goes through a process wherein NHPI functions as a catalyst rather than as an initiator. On the other hand, the hydrogen abstraction of the C-H bond conducted by a PINO species rather than the highly reactive N-centered radicals rationalizes the high chemoselectivity of the monochlorination obtained by this protocol as the latter is reactive towards the C(sp3)-H bonds of the monochlorides. The present results could hold promise for further development of a nitroxy-radical system for the highly selective functionalization of the aliphatic and benzylic hydrocarbon C-H.
- Li, Zi-Hao,Fiser, Béla,Jiang, Biao-Lin,Li, Jian-Wei,Xu, Bao-Hua,Zhang, Suo-Jiang
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supporting information
p. 3403 - 3408
(2019/04/01)
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- Highly selective halogenation of unactivated C(sp3)-H with NaX under co-catalysis of visible light and Ag@AgX
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The direct selective halogenation of unactivated C(sp3)-H bonds into C-halogen bonds was achieved using a nano Ag/AgCl catalyst at RT under visible light or LED irradiation in the presence of an aqueous solution of NaX/HX as a halide source, in air. The halogenation of hydrocarbons provided mono-halide substituted products with 95% selectivity and yields higher than 90%, with the chlorination of toluene being 81%, far higher than the 40% conversion using dichlorine. Mechanistic studies demonstrated that the reaction is a free radical process using blue light (450-500 nm), with visible light being the most effective light source. Irradiation is proposed to cause AgCl bonding electrons to become excited and electron transfer from chloride ions induces chlorine radical formation which drives the substitution reaction. The reaction provides a potentially valuable method for the direct chlorination of saturated hydrocarbons.
- Liu, Shouxin,Zhang, Qi,Tian, Xia,Fan, Shiming,Huang, Jing,Whiting, Andrew
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p. 4729 - 4737
(2018/10/23)
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- Mild Aliphatic and Benzylic Hydrocarbon C-H Bond Chlorination Using Trichloroisocyanuric Acid
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We present the controlled monochlorination of aliphatic and benzylic hydrocarbons with only 1 equiv of substrate at 25-30 °C using N-hydroxyphthalimide (NHPI) as radical initiator and commercially available trichloroisocyanuric acid (TCCA) as the chlorine source. Catalytic amounts of CBr4 reduced the reaction times considerably due to the formation of chain-carrying ·CBr3 radicals. Benzylic C-H chlorination affords moderate to good yields for arenes carrying electron-withdrawing (50-85%) or weakly electron-donating groups (31-73%); cyclic aliphatic substrates provide low yields (24-38%). The products could be synthesized on a gram scale followed by simple purification via distillation. We report the first direct side-chain chlorination of 3-methylbenzoate affording methyl 3-(chloromethyl)benzoate, which is an important building block for the synthesis of vasodilator taprostene.
- Combe, Sascha H.,Hosseini, Abolfazl,Parra, Alejandro,Schreiner, Peter R.
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p. 2407 - 2413
(2017/03/11)
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- Treatment of alcohols with tosyl chloride does not always lead to the formation of tosylates
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Treatment of substituted benzyl alcohols with tosyl chloride resulted in the formation of the corresponding chlorides, not the usual tosylates. A series of experiments demonstrated that it was possible to predict whether chlorination or tosylation would occur for substituted benzyl alcohols and pyridine methanols. Treatment of electron withdrawing group-substituted benzyl alcohols with tosyl chloride gave the corresponding chlorides in moderate yields under mild conditions, which provided a simple way to directly prepare chlorides from alcohols.
- Ding, Rui,He, Yong,Wang, Xiao,Xu, Jingli,Chen, Yurong,Feng, Man,Qi, Chuanmin
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experimental part
p. 5665 - 5673
(2011/09/20)
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- A duality of mechanisms for the fragmentation of substituted benzyloxychlorocarbenes
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Substituted benzyloxychlorocarbenes (X-PhCH2OCCl) were generated photochemically at 25 °C in dichloroethane from appropriate diazirine precursors. Fragmentations of the carbenes produced were determined by laser flash photolysis. The data (X, kfrag in s-1) were: p-Me, 2.6 × 105; p-Ph, 8.3 × 104; H, 6.0 × 104; p-Cl, 5.2 × 104; m-Cl, 1.3 × 105; p-F3C, 2.1 × 106; p-O2N, 6.3 × 106. A Hammett correlation of log kfrag versus σ+ was parabolic. The curvature was taken to imply the gradual change of the fragmentation mechanism from predominantly heterolytic for X-PhCH2CCl with electron-donating X (with developing positive charge on the benzylic carbon in the transition state) to predominantly homolytic for carbenes with electron-withdrawing X. This idea was supported by computational studies. Copyright
- Moss, Robert A.,Ma, Yan,Sauers, Ronald R.
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p. 13968 - 13969
(2007/10/03)
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- Gas-phase substituent effects in highly electron-deficient systems. II. stabilities of 1-aryl-2,2,2-trifluoroethyl cations based on chloride-transfer equilibria
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The relative stabilities of 1-aryl-2,2,2-trifluoroethyl cations were determined based on the chloride ion-transfer equilibria in the gas phase. An application of the Yukawa-Tsuno equation to this substituent effect on the equilibrium constants gave a remarkably larger r+ of 1.53 and a ρ of-10.6, supporting our previous conclusion that the highly electron-deficient benzylic carbocation systems are characterized by extremely high resonance demands. This r+ value, furthermore, conformed a linear relationship between the r+ value and the relative stability of the unsubstituted member of the respective benzylic carbocations, clearly demonstrating a continuous spectrum of varying resonance demands characteristic of the stabilities of carbocations. The π-delocalization of the positive charge into the aryl π-system increases with the destabilization of a carbocation by the α-substituent(s) linked to the central carbon. In addition, the r + value of 1.53 for 1-aryl-2,2,2-trifluoroethyl cations was found to be in complete agreement with that for the solvolysis of 1-aryl-2,2,2- trifluoroethyl tosylates in 80% aq acetone. This reveals that the r+ value observed for this solvolysis must be the intrinsic resonance demand of a highly electron-deficient cationic transition state in the SN 1 ionizing process. The identity of the r+ value was consistent with our previous observation for other benzylic carbocation systems, indicating that the degree of the π-delocalization of the positive charge is identical between the cationic transition state and an intermediate cation for all benzylic systems, which cover a wide range of reactivity and stability of the carbocation. This leads us to the conclusion that the geometry of the transition state in the ionizing process of the SN1 solvolysis, which is a highly endothermic reaction, closely resembles the high-energy product, an intermediate cation.
- Mishima, Masaaki,Inoue, Hiroki,Fujio, Mizue,Tsuno, Yuho
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p. 1163 - 1169
(2007/10/03)
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- Preparation of 2-(2-thienyl) ethylamine and synthesis of thieno [3,2-C] pyridine derivatives therefrom
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Compounds of the formulae:and wherein:, R1, R2, R3 and R4 are independently hydrogen, lower alkyl of one to six carbon atoms, aryl or substituted aryl;, are advantageously converted to isocyanurate compounds, 2-(2-thienyl)ethylamine compounds and thieno[3,2-c]pyridine derivatives and the pharmaceutically acceptable salts thereof, particularly ticlopidine hydrochloride.
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- Carbamate salts of 2-(2'-thienyl)alkylamines
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The carbamate salt of 2-(2'-thienyl)-alkylamines and particularly the ethylamine and its method of synthesis are disclosed. The carbamate salt of 2-(2'-thienyl)ethylamine is a stable, easily transportable crystalline material that can be converted to 2-(2'-thienyl)ethylamine, a useful intermediate in the synthesis of 5[(2-chlorophenyl)methyl]-4,5,6,7-tetrahydrothieno-[3,2-c]pyridine hydrochloride, also known as ticlopidine hydrochloride. The synthesis is carried out by reacting an amine of formula (I): STR1 with CO2 in a hydrocarbon solvent to obtain the carbamate salt of formula II: STR2
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- Versatility of Zeolites as Catalysts for Ring or Side-Chain Aromatic Chlorinations by Sulfuryl Chloride
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Zeolites catalyze chlorination of aromatics by sulfuryl chloride SO2Cl2.It is possible by an appropriate choice of the catalyst to effect at will, with very high selectivity, either the ring or the side-chain chlorination.Zeolite ZF520 is the choice catalyst for the former, because of its high Broensted acidity.Zeolite NaX (13X) is a fine catalyst for the latter, free-radical chlorination; the reaction is best effected in the presence of a light source; the catalyst can be reused many times with no loss in activity.Both reaction modes, the ionic (ring chlorination)and the radical (side-chain substitution), are likely to occur outside of the channel network in the microporous solid.The effects of various experimental factors - such as the nature of the solvent, the reaction time and temperature, the Broensted acidity of the solid support, the presence of radical inhibitors, and the quantity of catalysts - were investigated.The procedures resulting from this study are very easy to implement in practice and are quite effective.
- Delaude, Lionel,Laszlo, Pierre
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p. 5260 - 5269
(2007/10/02)
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- 2-(2-nitrovinyl)thiophene reduction and synthesis of thieno[3,2-c]pyridine derivatives
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An improved process for the reduction of 2-(2-nitrovinyl)thiophene to form 2-(2-thienyl)ethylamine employs a boron-containing reducing agent, preferably diborane. The 2-(2-thienyl)ethylamine produced by this process is advantageously converted to ticlopidine.
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- MECHANISMS OF FREE-RADICAL REACTIONS. XX. REACTIVITY IN THE FREE-RADICAL HALOGENATION REACTIONS OF ARYLFLUOROALKANES
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The free-radical chlorination and bromination of meta- and para-substituted benzyl fluorides and 1,1-difluoro-2-phenylethane and also the chlorination of 1-fluoro-2-arylethanes by phenylchloroiodonium chloride and the bromination of meta- and para-substituted benzyl bromides were studied by the method of competing reactions.In all cases a good correlation is observed between log krel and the Brown ?+ constants.In cases where change in the reactivity in the transition from one reaction series to another is due mainly to the polar effect of the substituent whilethe selectivity is measured in relation to the polar effect direct relationships are observed between the reactivity and the selectivity.
- Dneprovskii, A. S.,Eliseenkov, E. V.
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p. 711 - 719
(2007/10/02)
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- Chlorination of Toluene and Substituted Toluenes by Trichloroisocyanuric Acid: A Kinetic Investigation
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The kinetics of chlorination of toluene, o-, m- and p-xylenes, m- and p-chlorotoluenes and m-nitrotoluene by trichloroisocyanuric acid (TCCA) in aqueous acetic acid in the presence of perchloric acid (HClO4) have been studied.The reaction is first order each in and .The reaction is insensitive towards change in .Increase in the percentage of acetic acid in the reaction medium retards the reaction rate.Various thermodynamic parameters have been evaluated.A suitable mechanism is postulated taking the observed kinetic data into consideration.
- Pati, Subas C.,Sarangi, Chintamani
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p. 745 - 747
(2007/10/02)
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- Structure-activity studies on antihyperlipidemic N-benzoylsulfamates, N-benzylsulfamates, and benzylsulfonamides
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A series of aryl substituted N-benzoyl- and N-benzylsulfamic acid sodium salts and benzylsulfonamide sodium salts have been prepared and examined for antihyperlipidemic activity in male CF1 mice at a dose level of 20 mg/kg/d ip for 16 d. These substances were also subjected to toxicological evaluation and chemical stability studies. In general, both series of sulfamates and sulfonamides significantly lowered serum cholesterol and triglyceride levels in mice. The compounds were nonmutagenic, showed no acute toxicity or impaired liver or kidney function in male mice, and were chemically stable both as the monohydrates and in aqueous solution over a pH range of 3.5-7.4. While both series of sulfamates and sulfonamides lowered serum cholesterol and triglyceride levels, the sulfamates were relatively more potent with regard to decreasing cholesterol levels, while the sulfonamides were more effective in lowering serum triglyceride levels in mice.
- Wyrick,Hall,Dubey
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p. 374 - 377
(2007/10/02)
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- Mechanisms of free-radical reactions. XI. Kinetic investigation of the free-radical chlorination of alkyl aromatic hydrocarbons by phenylchloroiodonium chloride
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The free-radical chlorination of meta- and para-substituted toluenes, ethylbenzene, and cumenes by phenylchloroiodonium chloride was investigated by the method of competing reactions.The good correlation between the relative reaction rate constants and the Brown ?+ constants and also the large negative values of ρ indicate separation of charges in the transition state.The values of the primary kinetic isotope effects of hydrogen decrease with increase in the reactivity of the substrate, whereas the values of the reaction parameters vary irregularly.The deviations from the inverse relation between the reactivity and the selectivity are due to the polar character of the transition state.
- Dneprovskii, A. S.,Kasatochkin, A. N.
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p. 693 - 699
(2007/10/02)
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