- Synthesis and evaluation of tetrahydroisoquinoline derivatives against Trypanosoma brucei rhodesiense
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Human African Trypanosomiasis (HAT) is a neglected tropical disease caused by the parasitic protozoan Trypanosoma brucei (T. b.), and affects communities in sub-Saharan Africa. Previously, analogues of a tetrahydroisoquinoline scaffold were reported as having in vitro activity (IC50 = 0.25–70.5 μM) against T. b. rhodesiense. In this study the synthesis and antitrypanosomal activity of 80 compounds based around a core tetrahydroisoquinoline scaffold are reported. A detailed structure activity relationship was revealed, and five derivatives (two of which have been previously reported) with inhibition of T. b. rhodesiense growth in the sub-micromolar range were identified. Four of these (3c, 12b, 17b and 26a) were also found to have good selectivity over mammalian cells (SI > 50). Calculated logD values and preliminary ADME studies predict that these compounds are likely to have good absorption and metabolic stability, with the ability to passively permeate the blood brain barrier. This makes them excellent leads for a blood-brain barrier permeable antitrypanosomal scaffold.
- Cullen, Danica R.,Gallagher, Ashlee,Duncan, Caitlin L.,Pengon, Jutharat,Rattanajak, Roonglawan,Chaplin, Jason,Gunosewoyo, Hendra,Kamchonwongpaisan, Sumalee,Payne, Alan,Mocerino, Mauro
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- 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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- 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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- Improved Halogenation of Methyl Aromatics and Methyl Heteroaromatics: Unexpected Reactivity of Tetrahalogeno-diphenylglycolurils
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1,3,4,6-Tetrachloro (TCDGU) and 1,3,4,6-tetrabromo-3α,6α-diphenylglycolurils smooth halogen oxidizers have been exploited in a new direction as reagents for free radical substitution toward some N-halosuccinimide nonreactive bis-heterocycles. An unexpected selectivity and reactivity were observed with methyl benzenes, methyl heterocycles, and methyl-bis-heterocycles of interest. A chemometric study has been performed to optimize five independent factors of the chlorination reaction with TCDGU. The predictive model was established either for the halogenation conversion and the ratio of monochlorination.
- Moretti, Florian,Poisson, Guillaume,Marsura, Alain
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p. 173 - 183
(2016/05/19)
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- Iron catalyzed halogenation of benzylic aldehydes and ketones
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A simple and efficient iron-catalyzed method for chlorination of aromatic carbonyl compounds is reported. By using 4-10 mol% Fe(iii) oxo acetate catalyst, prepared by solid state atmospheric oxidation of Fe(ii) acetate, in combination with triethylsilane and chlorotrimethylsilane, hydrosilylation of benzylic carbonyl compounds with subsequent chlorination is achieved within a few hours at room temperature. This new method is mild and rapid compared to the conventional two step approach involving reduction and chlorination reactions in separate stages. Development of synthetic methodology is also supplemented here by kinetic investigation of the reaction mechanism, which supports the tentative mechanisms suggested previously for similar reactions. This journal is
- Savela, Risto,W?rn?, Johan,Murzin, Dmitry Yu.,Leino, Reko
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p. 2406 - 2417
(2015/04/14)
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- Regiospecific chlorination of xylenes using K-10 montmorrillonite clay
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Regiospecific chlorination of xylenes has been developed by employing NCS as a reagent and K-10 montmorrillonite clay as a solid support. Copyright Taylor & Francis Group, LLC.
- Thirumamagal,Narayanasamy, Sureshbabu,Venkatesan
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scheme or table
p. 2820 - 2825
(2009/05/07)
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- Efficient synthesis of tolunitriles by selective ammoxidation
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Tolunitriles have been efficiently synthesized by selective ammoxidation of methylbenzyl chlorides prepared with chlorination of xylenes. In comparison with ammoxidation of xylenes themselves, the reaction temperature of ammoxidation of methylbenzyl chlorides has been lowered more than 100°C and the selectivity forming mono-nitriles is almost 100%.
- Xie, Guangyong,Zheng, Qiong,Huang, Chi,Chen, Yuanyin
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p. 1103 - 1107
(2007/10/03)
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- Interpretation of retention indices in gas chromatography for establishing structures of isomeric products of alkylarenes radical chlorination
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By an example of previously uncharacterized products obtained by alkylarenes radical chlorination was demonstrated that combination of various interpretation methods applied to the retention indices (RI) in the gas chromatography on the standard nonpolar phases (comparison of RI of products and initial compounds, characteristics of succession of the chromatographic elution of the structural isomers with the use of estimation of molecular dynamic parameters, application of the additive schemes to RI calculation, and using of structural analogy CH3?Cl for testing the results obtained) permitted unambiguous identification of the structure even without data of mass spectrometry.
- Zenkevich
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p. 270 - 280
(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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- Electrophilic Aromatic Substitution. 13.1 Kinetics and Spectroscopy of the Chloromethylation of Benzene and Toluene with Methoxyacetyl Chloride or Chloromethyl Methyl Ether and Aluminum Chloride in Nitromethane or Tin Tetrachloride in Dichloromethane. the Methoxymethyl Cation as a Remarkably Selective Common Electrophile
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Vacuum line kinetics studies have been made of the reaction in nitromethane between benzene and/or toluene, methoxyacetyl chloride (MAC), and AlCl3 to produce benzyl or xylyl chlorides, CO, and a CH3OH- AlCl3 complex. For both arenes, the rate law appears to be R = (k3/[AlCl3]0) [AlCl3]2-[MAC]. When chloromethyl methyl ether (CMME) is substituted for MAC, a similar rate law is obtained. Both chloromethylation reactions yielded similar, large kT/kB ratios (500-600) and similar product isomer distributions with low meta percentages (～0.4) which suggest CH3OCH2+ or the CH3OCH2+Al2Cl7 - ion pair as a common, remarkably selective, electrophile. The kinetics of MAC decomposition to CMME and CO in the presence of AlCl3 yielded the rate law R = k2[AlCl3]0[MAC]. Here AlCl3 is a catalyst (no CH3OH is formed), and thus the rate law is equivalent to the chloromethylation rate law. All three reactions have comparable reactivities, which is consistent with rate-determining production of the electrophile. Kinetics studies of benzene or toluene with SnCl4 and MAC or CMME in dichloromethane were also completed. With MAC and benzene the rate law is R = k3[SnCl4]0[MAC][benzene] and with toluene R = k2[SnCl4]0[MAC]. MAC decomposition, again followed by CO production, was unaffected by the presence of either aromatic and obeyed the rate law R = k2′ [SnCl4]0[MAC] where k2 ≈ k2′ Chloromethylation with CMME followed the rate law R = k3[SnCl4]0[CMME][arene] for benzene and toluene and produced a kT/kB ratio and product isomer distributions very similar to those determined with AlCl3 in nitromethane, further supporting a common electrophile. Low-temperature 13C and 119Sn FT-NMR and Raman spectroscopic studies suggest the existence of a weak 1:1 adduct between MAC and SnCl4 of the type RCXO → SnCl4, with electron donation to the metal through carboxy oxygen. Finally, an explanation is provided for the range of chloromethylation kT/kB values and product isomer percentages published in the literature.
- Dehaan, Franklin P.,Djaputra, Markus,Grinstaff, Mark W.,Kaufman, Craig R.,Keithly, James C.,Kumar, Amit,Kuwayama, Mark K.,Dale Macknet,Na, Jim,Patel, Bimal R.,Pinkerton, Michael J.,Tidwell, Jeffrey H.,Villahermosa, Randy M.
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p. 2694 - 2703
(2007/10/03)
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- Mechanistic and synthetic aspects of a novel route to poly-p-xylylene (PPX) via nickel complex catalysed electropolymerisation of 1,4-bis(chloromethyl)benzene
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It is shown that in the presence of catalytic amounts of NiIICl2L2 (L2 = dppe or dppp) 1,4-bis(chloromethyl)benzene is electrochemically reduced to poly-p-xylylene (PPX). Cyclic voltammetric examination of this reaction, and of the analogous conversion of benzyl chloride into bibenzyl, is combined with the construction of reactant/product vs. charge profiles to develop a detailed mechanistic description. There is compelling evidence that, in contrast with the established cathodic formation of PPX from 1,4-bis(halomethyl)benzene via electrogenerated quinodimethane (xylylene), the Ni complex catalysed route involves oxidative addition of the halide derivative to Ni0L2.
- Amatore, Christian,Gaubert, Florence,Jutand, Anny,Utley, James H. P.
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p. 2447 - 2452
(2007/10/03)
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- Selective Cross Coupling via Oxovanadium(V)-Induced Oxidative Desilylation of Benzylic Silanes
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Benzylic silanes bearing an electron-donating group at the ortho- or para-position underwent the oxovanadium(V)-induced one-electron oxidative desilylation due to low ionization potential, which was applied to the intermolecular regioselective coupling with allylic silanes or silyl enol ether.
- Hirao, Toshikazu,Fujii, Takashi,Ohshiro, Yoshiki
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p. 8005 - 8008
(2007/10/02)
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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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- Halogenation of benzyl- and (heteroaromatic methyl)cobaloximes: Direct competition between ring halogenation and cobalt-carbon bond cleavage
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(4-Acetamidobenzyl)- and (4-(dimethylamino)benzyl)cobaloximes react rapidly with low concentrations of chlorine and bromine in acetic acid or chloroform at room temperature under nitrogen. Both ring-halogenated organometallic products and direct Co-C cleavage products are formed. However, (4-methoxybenzyl)cobaloxime forms 4-methoxy-2-halotoluene as the exclusive product. (3-Methylbenzyl)cobaloxime undergoes a substantial proportion of ring substitution by both Br2 and Cl2 in competition with the cleavage of the Co-C bond. (3-Methoxybenzyl)cobaloxime forms only the ring-substituted organometallic product. A remarkable difference in reactivity between 2- and 3-isomers of the (thienylmethyl)- and (furylmethyl)cobaloximes is observed; for example, Co-C cleavage is the primary process in furfuryl- and (2-thienylmethyl)cobaloximes whereas ring halogenation occurs much faster in the 3-isomer. The results are discussed in terms of a σ-π delocalization phenomenon by which the electronic effect of a substituent in the benzyl group is effectively transmitted to the Co-C bond reactivity. The substituent effect of the metallomethyl group -CH2Co(dmgH)2py is found to be more than that of the methoxy group. The mechanism of the Co-C cleavage is described.
- Gupta,Kumar, Manoj,Roy, Sujit
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- Kinetics and Equilibria of Chloride Transfer Reactions. Stabilities of Carbocations Based on Chloride and Hydride Transfer Equilibria Measurements
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The kinetics of a number of gas-phase chloride transfer reactions R0(1+)+RCl=R0Cl+R(1+) were measured with a pulsed electron high pressure mass spectrometer.Most of the reactions were found to occur near the collision limit, i.e., with rate constants k ca. 10-9 molecules-1 cm3 s-1.However, several reactions were much slower and were exhibiting negative temperature dependence, i.e., decreasing rate with increasing temperature.Hydride and chloride transfer equilibria were determined for various carbocations R(1+) (R=isopropyl, cyclopentyl, tert-butyl, 1-methylcyclopentyl, substituted benzyls, norbornyl, 2-methyl-2-norbornyl, and adamantyl).Excellent agreement with earlier hydride transfer measurements of Solomon, Meot-Ner, and Field were observed.The chloride affinities generally support conclusions based on the hydride transfer data.Discussion of the data in connection with benzyl cation substituent effects, the norbornyl cation stability, and solvent effects on carbocation stability is presented.The data show that the 2-norbornyl cation is unusually stable.Significant differences between carbocation R(1+) stabilities in gas phase and solution are found which suggest that both differential nucleophilic solvent stabilization and differential nonspecific solvation occur in solution.
- Sharma, R. B.,Sharma, D. K. Sen,Hiraoka, K.,Kebarle, P.
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p. 3747 - 3757
(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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- 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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- Regioselective Ring Opening in Substituted Benzocyclopropenes. An Alternative or Complementary Mechanism for Electrophilic Substitution Involving Attack at a ? Bond
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2-Methylbenzocyclopropene (5) reacts with bromine, iodine, and HCl to give the m-xylenes 12a,c,d as the major products, whereas it reacts with silver nitrate in the presence of ethanol and aniline to give the o-xylenes 11e,f as the major products.Similarly, 3-methylbenzocyclopropene (10) gives mainly m-xylenes 14a,c,d with halogens and HCl and gives p-xylenes 13e,f with silver nitrate and ethanol or aniline.Cyclopropabenzocyclobutene (15) also gives different products with halogens and silver nitrate, but in this case HCl gives the same type of product as the silver ion.The difference in electrophilic behavior of 5, 10, and 15 toward the two types of reagents is suggested to arise from attack of the silver ion (and the proton in the case of 15) on the ? electrons of the cyclopropyl ring.
- Bee, Lim Keow,Garratt, Peter J.,Mansuri, Muzamil M.
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p. 7076 - 7079
(2007/10/02)
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- Electronic Spectra and Electron Affinity of Monomethyl- and Dimethyl-Substituted Benzyl Radicals
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Three monomethylbenzyl radicals and five dimethylbenzyl radicals have been authentically generated by the dissociative electron attachment to corresponding methyl-substituted benzyl chlorides in γ-irradiated glassy matrices and studied by the fluorescence spectrophotometric method at 77 K.For the radicals in a polar ethanol matrix where they are free from the chloride counterion, the wavelengths for the O-O bands of the fluorescence spectra and of the fluorescence-excitation spectra (to the third excited state, in 320-330-nm region) have been determined.These results revise the previous assignment of the spectra of 2,4- and 3,4-dimethylbenzyl radicals.In a nonpolar 3-methylhexane matrix, the association of the counterion with the radicals causes the change in vibrational structures, as well as the shifts of the spectra due to the radicals, and the appearance of a charge-transfer band due to the chloride ion-radical pairs.From the transition energies of the CT bands, the electron affinities have been determined for all eight methyl-substituted benzyl radicals with reference to the reported electron affinity of the benzyl radical.These experimental electron affinities are in general agreement with those calculated theoretically within the INDO approximation.It has been also found that the photolysis of substituted and unsubstituted benzyl chlorides at 77 K results in the rupture of a C-H bond as well as a C-Cl bond, so that several isomeric benzyl-type radicals are generated simultaneously.
- Izumida, Tatsuo,Ichikawa, Tsuneki,Yoshida, Hiroshi
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- CHARACTERISTICS OF THE INITIATED (RADICAL) CHLORINATION OF m-XYLENE
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By GLC it was established that the composition of the products from initiated chlorination of m-xylene is determined by the molar ratio of the reagents (m-xylene and chlorine).An assessment of the reactivity of the individual chlorine derivatives of m-xylene is given.
- Kosheleva, L. M.,Rozenberg, V. R.,Motsarev, G. V.
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p. 1607 - 1610
(2007/10/02)
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