- One-Pot Deoxygenation and Substitution of Alcohols Mediated by Sulfuryl Fluoride
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Sulfuryl fluoride is a valuable reagent for the one-pot activation and derivatization of aliphatic alcohols, but the highly reactive alkyl fluorosulfate intermediates limit both the types of reactions that can be accessed as well as the scope. Herein, we report the SO2F2-mediated alcohol substitution and deoxygenation method that relies on the conversion of fluorosulfates to alkyl halide intermediates. This strategy allows the expansion of SO2F2-mediated one-pot processes to include radical reactions, where the alkyl halides can also be exploited in the one-pot deoxygenation of primary alcohols under mild conditions (52-95% yield). This strategy can also enhance the scope of substitutions to nucleophiles that are previously incompatible with one-pot SO2F2-mediated alcohol activation and enables substitution of primary and secondary alcohols in 54-95% yield. Chiral secondary alcohols undergo a highly stereospecific (90-98% ee) double nucleophilic displacement with an overall retention of configuration.
- Epifanov, Maxim,Mo, Jia Yi,Dubois, Rudy,Yu, Hao,Sammis, Glenn M.
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p. 3768 - 3777
(2021/03/01)
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- Discovery of Aryl Formyl Piperidine Derivatives as Potent, Reversible, and Selective Monoacylglycerol Lipase Inhibitors
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Most of the current monoacylglycerol lipase (MAGL) inhibitors function by an irreversible mechanism of action, causing a series of side effects. Herein, starting from irreversible inhibitors, 25 compounds were synthesized and evaluated in vitro for MAGL inhibition, among which, compound 36 showed the most potent inhibitory activity (IC50 = 15 nM). Crucially, docking studies demonstrated that the m-chlorine-substituted aniline fragment occupied a hydrophobic subpocket enclosed by side chains of Val191, Tyr194, Val270, and Lys273, which creatively identify a new key anchoring point for the development of new MAGL inhibitors. Furthermore, in vivo evaluation innovatively revealed that this reversible inhibitor 36 significantly ameliorated depressive-like behaviors induced by reserpine. To the best of our knowledge, this is the first time that reversible inhibitors of MAGL were developed to support MAGL as a potential therapeutic target for depression.
- Zhi, Zhuoer,Zhang, Wenting,Yao, Jingchun,Shang, Yanguo,Hao, Qingjing,Liu, Zhong,Ren, Yushan,Li, Jie,Zhang, Guimin,Wang, Jinxin
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p. 5783 - 5796
(2020/07/14)
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- Understanding the effects of ionic liquids on a unimolecular substitution process: Correlating solvent parameters with reaction outcome
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A unimolecular substitution process was studied in five different ionic liquids, with systematic variation of either the cation or anion, in order to determine the factors leading to the increase in the rate constant for the process relative to acetonitrile. It was found that both components of the ionic liquid, and the proportion of the salt in the reaction mixture, affect the rate constant. Activation parameters determined for the process suggest that there is a balance between interactions of the components of the ionic liquid with both starting material and transition state. A correlation was found between the rate constant and a combination of Kamlet-Taft solvent parameters; with the polarisability of the solvent being the most significant factor. As this reaction proceeds through both unimolecular and bimolecular pathways, competition experiments determined that the unimolecular pathway for the reaction can be favoured using small amounts of ionic liquid in the reaction mixture, demonstrating the potential to control reaction mechanisms using ionic liquids.
- Gilbert, Alyssa,Haines, Ronald S.,Harper, Jason B.
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supporting information
p. 675 - 682
(2019/01/24)
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- Organic synthesis in a modular robotic system driven by a chemical programming language
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The synthesis of complex organic compounds is largely a manual process that is often incompletely documented. To address these shortcomings, we developed an abstraction that maps commonly reported methodological instructions into discrete steps amenable to automation. These unit operations were implemented in a modular robotic platform by using a chemical programming language that formalizes and controls the assembly of the molecules. We validated the concept by directing the automated system to synthesize three pharmaceutical compounds, diphenhydramine hydrochloride, rufinamide, and sildenafil, without any human intervention. Yields and purities of products and intermediates were comparable to or better than those achieved manually. The syntheses are captured as digital code that can be published, versioned, and transferred flexibly between platforms with no modification, thereby greatly enhancing reproducibility and reliable access to complex molecules.
- Steiner, Sebastian,Wolf, Jakob,Glatzel, Stefan,Andreou, Anna,Granda, Jaros?aw M.,Keenan, Graham,Hinkley, Trevor,Aragon-Camarasa, Gerardo,Kitson, Philip J.,Angelone, Davide,Cronin, Leroy
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- Visible-light-mediated benzylic sp3 C-H bond functionalization to C-Br or C-N bond
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A visible-light-promoted functionalization of unactivated benzylic sp3 C-H bonds was developed. Ethylbenzene derivatives were converted to the corresponding benzyl bromides or afforded benzylamine derivatives in a one-pot manner under visible light photoredox conditions.
- Hou, Tianyuan,Lu, Ping,Li, Pixu
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supporting information
p. 2273 - 2276
(2016/05/10)
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- The effects of an ionic liquid on unimolecular substitution processes: The importance of the extent of transition state solvation
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The reaction of bromodiphenylmethane and 3-chloropyridine, which proceeds concurrently through both unimolecular and bimolecular mechanisms, was examined in mixtures of acetonitrile and an ionic liquid. As predicted, the bimolecular rate constant (k2) gradually increased as the amount of ionic liquid in the reaction mixture increased, as a result of a minor enthalpic cost offset by a more significant entropic benefit. Addition of an ionic liquid had a substantial effect on the unimolecular rate constant (k1) of the reaction, with at least a 5-fold rate enhancement relative to acetonitrile, which was found to be due to a significant decrease in the enthalpy of activation, partially offset by the associated decrease in the entropy of activation. This is in contrast to the effects seen previously for aliphatic carbocation formation, where the entropic cost dominated reaction outcome. This change is attributed to a lessened ionic liquid-transition state interaction, as the incipient charges in the transition state were delocalized across the neighbouring π systems. By varying the mole fraction of ionic liquid in the reaction mixture the ratio between k1and k2could be altered, highlighting the potential to use ionic liquids to control which pathway a reaction proceeds through.
- Keaveney, Sinead T.,White, Benjamin P.,Haines, Ronald S.,Harper, Jason B.
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supporting information
p. 2572 - 2580
(2016/03/01)
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- Catalytic Carbocation Generation Enabled by the Mesolytic Cleavage of Alkoxyamine Radical Cations
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A new catalytic method is described to access carbocation intermediates via the mesolytic cleavage of alkoxyamine radical cations. In this process, electron transfer between an excited state oxidant and a TEMPO-derived alkoxyamine substrate gives rise to a radical cation with a remarkably weak C?O bond. Spontaneous scission results in the formation of the stable nitroxyl radical TEMPO.as well as a reactive carbocation intermediate that can be intercepted by a wide range of nucleophiles. Notably, this process occurs under neutral conditions and at comparatively mild potentials, enabling catalytic cation generation in the presence of both acid sensitive and easily oxidized nucleophilic partners.
- Zhu, Qilei,Gentry, Emily C.,Knowles, Robert R.
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supporting information
p. 9969 - 9973
(2016/08/16)
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- Synthesis of multisubstituted indenes via iron-catalyzed domino reaction of benzylic compounds and alkynes
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A novel approach to synthesizing multisubstituted indenes by iron-catalyzed domino reaction of benzylic compounds and alkynes under mild conditions was developed. This system could be applied to various available substrates in a one-step synthetic procedure in moderate to good yields. Georg Thieme Verlag Stuttgart · New York.
- Chen, Yongxin,Li, Kangning,Liu, Xiang,Zhu, Jiaoyan,Chen, Baohua
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supporting information
p. 130 - 134
(2013/02/25)
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- In situ generated Ph3P(OAc)2as a novel reagent for the efficient acetylation of alcohols and thiols at room temperature
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Ph3P, Br2, and ammonium acetate are used for the in situ generation of Ph3P(OAc)2, which was characterized by different NMR techniques. The Ph3P(OAc)2generated was used as a novel and efficient reagent for the acetylation of alcohols and thiols in acetonitrile at room temperature under homogeneous conditions. This reaction was also performed under heterogeneous conditions using 1,3,2,4- diazadiphosphetidine as an easily prepared, stable, and heterogeneous P(III) compound.
- Iranpoor, Nasser,Firouzabadi, Habib,Elham, Etemadi Davan
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p. 1813 - 1816
(2013/04/24)
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- Synthesis of silica bromide as heterogeneous reagent and its application to conversion of alcohols to alkyl bromides
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Silica bromide as heterogeneous reagent is prepared from the reaction of silica gel with PBr3 as a nonhydroscopic, filterable, cheap, and stable yellowish powder that can be stored for months. The results show that the silica bromide is a suitable and efficient reagent for conversion of alcohols to alkyl bromides under mild conditions at room temperature. The easy availability of this reagent makes this simple procedure attractive and a practical alternative to the existing methods.
- Mohanazadeh, Farajollah,Sedrpoushan, Alireza,Zolfigol, Mohammad A.,Veisi, Hojat
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p. 598 - 603,6
(2012/12/11)
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- Polyvinylpyrrolidone-bromine complex: An efficient polymeric reagent for selective preparation of benzyl bromides in the presence of hexamethyldisilane
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Benzylic bromides were conveniently obtained in high yields via the reaction of the corresponding alcohols with crosslinked polyvinylpyrrolidone- bromine complex (PVPP-Br2)/hexamethyldisilane in chloroform at reflux condition. Selective conversion of benzyl alcohol to benzyl bromide in the presence of primary aliphatic alcohols, e.g. 2-phenylethanol was also achieved.
- Mokhtary, Masoud,Lakouraj, Moslem M.
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p. 305 - 309
(2012/10/29)
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- Synthesis and anticonvulsant activity of some cinnamylpiperazine derivatives
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A series of cinnamylpiperazine derivatives was synthesized using different benzophenone as starting material. The structures of the compounds were proved by their IR, 1H-NMR spectroscopic data and mass spectra data. The anticonvulsant activities of these compounds were evaluated with maximal electroshock (MES) test and rotarod test with intraperitoneal injection on KunMing mice. Among all the flunarizine analogues, no one exhibited better anticonvulsant activity than flunarizine. Flunarizine (4i) exhibited anticonvulsant activity with ED50 of 38.1 mg/kg, TD50 of 164.3 mg/kg and PI of 4.3 through administration intraperitoneal, and with ED50 of 56.8 mg/kg, TD50 of 456.3 mg/kg and PI of 8.0 through oral administration.
- Hu, Chuan,Sun, Zhi-Gang,Wei, Cheng-Xi,Quan, Zhe-Shan
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scheme or table
p. 661 - 664
(2011/11/29)
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- Can one predict changes from SN1 to SN2 mechanisms?
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The reactions of substituted benzhydryl bromides Ar2CHBr with primary and secondary amines in DMSO yield benzhydryl amines Ar 2CHNRR′, benzophenones Ar2CdO, and benzhydrols Ar2CHOH. Kinetic investigations at 20°C revealed the rate law -d[Ar2CHBr]/dt = (k1 + k2[HNRR′])[Ar 2CHBr], where the amine independent term k1 gave rise to the formation of Ar2CdO and Ar2CHOH and the amine-dependent term k2[HNRR′] was responsible for the formation of Ar2CHNRR′. Clear evidence for concomitant S N1 and SN2 processes was obtained. While the rate constants of the SN1 reactions correlate with Hammett's σ+ constants (ρ = -3.22), the second-order rate constants k2 for the SN2 reactions are not correlated with the electron releasing abilities of the substituents, indicating that the transition states of the SN2 reactions do not merge with the transition states of the SN1 reactions. The correlation equation log k 20°C = s(E + N), where nucleophiles are characterized by N and s and electrophiles are characterized by E (J. Am. Chem. Soc. 2001, 123, 9500-9512), was used to calculate the lifetimes of benzhydrylium ions in the presence of amines and DMSO. The change from SN1 to SN2 mechanism occurred close to the point where the calculated rate constant for the collapse of the benzhydrylium ions with the amines just reaches the vibrational limit; that is, the concerted SN2 mechanism was only followed when it was enforced by the lifetime of the intermediate. The nucleophile-specific parameters N and s needed for this analysis were determined by studying the kinetics of the reactions of a variety of amines with amino-substituted benzhydrylium tetrafluoroborates (Ar2CH+BF4-) of known electrophilicity E in DMSO. Analogously, the rates of the reactions of laser flash photolytically generated benzhydrylium ions Ar2CH + with DMSO in acetonitrile were employed to determine the nucleophile-specific parameters N and s of DMSO, and it is reported that DMSO is a significantly stronger O-nucleophile than water and ordinary alcohols.
- Thanh, Binh Phan,Nolte, Christoph,Kobayashi, Shinjiro,Ofial, Armin R.,Mayr, Herbert
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supporting information; experimental part
p. 11392 - 11401
(2011/02/27)
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- The aerobic oxidation of alcohols with a ruthenium porphyrin catalyst in organic and fluorinated solvents
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Carbonylruthenium tetrakis(pentafluorophenyl)porphyrin Ru(TPFPP)(CO) was utilized for the aerobic oxidation of alcohols. The in situ activation of the catalyst with mCPBA provided a species capable of catalyzing the oxidation of alcohols with molecular oxygen. The choice of solvent and additive was crucial to obtaining high activity and selectivity. Secondary aromatic alcohols were oxidized in the presence of the ruthenium porphyrin and tetrabutyl ammonium hydroxide in the solvent bromotrichloromethane, enabling high yields to be achieved (up to 99%). Alternatively, alcohols could be oxidized in perfluoro(methyldecalin) with the ruthenium porphyrin at higher temperatures (140 °C) and elevated oxygen pressures (50 psi). The Royal Society of Chemistry.
- Korotchenko, Vasily N.,Severin, Kay,Gagne, Michel R.
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scheme or table
p. 1961 - 1965
(2009/01/31)
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- 4-Aminophenyldiphenylphosphinite (APDPP), a new heterogeneous and acid scavenger phosphinite - Conversion of alcohols, trimethylsilyl, and tetrahydropyranyl ethers to alkyl halides with halogens or N-halosuccinimides
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A new heterogeneous phosphinite, 4-aminophenyldiphenylphosphinite (APDPP), is prepared and used for the efficient conversion of alcohols, trimethylsilyl ethers, and tetrahydropyranyl ethers to their corresponding bromides, iodides, and chlorides in the presence of molecular halogens or N-halosuccinimides. The amino group in this phosphinite acts as an acid scavenger and removes the produced acid. A simple filtration easily removes the phosphinate by-product.
- Iranpoor, Nasser,Firouzabadi, Habib,Gholinejad, Mohammad
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p. 1006 - 1012
(2007/10/03)
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- A new diphenylphosphinite ionic liquid (IL-OPPh2) as reagent and solvent for highly selective bromination, thiocyanation or isothiocyanation of alcohols and trimethylsilyl and tetrahydropyranyl ethers
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A new diphenylphosphinite ionic liquid (IL-OPPh2) is introduced. This ionic liquid is used as both a reagent and a solvent to convert alcohols and trimethylsilyl and tetrahydropyranyl (THP) ethers into their corresponding alkyl bromides, thiocyanates or isothiocyanates in the presence of Br2 and SCN- at 80 °C. In this ionic liquid, bromination and thiocyanation of alcohols occurs highly selectively in the presence of trimethylsilyl and THP-ethers and also between different classes of alcohols. The use of this ionic liquid allows easy separation of the desired products from the phosphinate by-product.
- Iranpoor, Nasser,Firouzabadi, Habib,Azadi, Roya
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p. 5531 - 5534
(2007/10/03)
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- Facile conversion of alcohols into their bromides and iodides by N-bromo and N-iodosaccharins/triphenylphosphine under neutral conditions
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N-Bromo and N-iodosaccharins in the presence of triphenylphosphine convert alcohols into the corresponding bromides and iodides in good to excellent yields at room temperature under neutral conditions.
- Firouzabadi, Habib,Iranpoor, Nasser,Ebrahimzadeh, Farzaneh
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p. 1771 - 1775
(2007/10/03)
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- Kinetics of the solvolyses of benzhydryl derivatives: Basis for the construction of a comprehensive nucleofugality scale
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A series of 21 benzhydrylium ions (diarylmethylium ions) are proposed as reference electrofuges for the development of a general nucleofugality scale, where nucleofugality refers to a combination of leaving group and solvent. A total of 167 solvolysis rate constants of benzhydrylium tosylates, bromides, chlorides, trifluoroacetates, 3,5-dinitrobenzoates, and 4-nitroben-zoates, two-thirds of which have been determined during this work, were subjected to a least-squares fit according to the correlation equation log k 25°C = Sf(Nf + Ef), where s f and Nf are nucleofuge-specific parameters and E f is an electrofuge-specific parameter. Although nucleofuges and electrofuges characterized in this way cover more than 12 orders of magnitude, a single set of the parameters, namely sf, Nf, and E f, is sufficient to calculate the solvolysis rate constants at 25°C with an accuracy of ± 16%. Because sf ≈ 1 for all nucleofuges, that is, leaving group/ solvent combinations, studied so far, qualitative discussions of nucleofugality can be based on Nf.
- Denegri, Bernard,Streiter, Andre,Juric, Sandra,Ofial, Armin R.,Kronja, Olga,Mayr, Herbert
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p. 1648 - 1656
(2007/10/03)
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- Kinetics of the reactions of halide anions with carbocations: Quantitative energy profiles for SN1 reactions
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Rate constants for the reactions of Laser flash photolytically generated benzhydrylium ions (diarylcarbenium ions) with halide ions have been determined in various solvents, including neat and aqueous acetonitrile as well as some alcohols. Substitution of the rate constants into the correlation equation log k = s(N + E) yields the nucleophilicity parameters N for the halide ions in different solvents. Linear correlations with negative slopes are found between the nucleophilicity parameters N for Cl- and Br- in different solvents and the solvent ionizing powers Y of the corresponding solvents. Increasing halide solvation reduces the rates of carbocation/chloride combinations by approximately half as much as it increases the rates of ionizations of benzhydryl chlorides. Comparison of the solvent dependent nucleophilicity parameters N of halide anions and the nucleophilicity parameters N1 for solvents yields a quantitative prediction of common ion rate depression, as demonstrated by the analysis of a variety of literature reported mass-law constants α. Combination of the rate constants for the reactions of benzhydrylium ions with halide ions (k-1) reported in this work with the ionization constants of benzhydryl halides (k1) and the recently reported rate constants for the reactions of benzhydrylium ions with solvents (k2) yields complete quantitative free energy profiles for solvolysis reactions. The applicability of Hammond's postulate for interpreting solvolysis reactions can thus be examined quantitatively.
- Minegishi, Shinya,Loos, Robert,Kobayashi, Shinjiro,Mayr, Herbert
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p. 2641 - 2649
(2007/10/03)
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- Silicaphosphine (Silphos): A filterable reagent for the conversion of alcohols and thiols to alkyl bromides and iodides
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Silicaphosphine (Silphos), [P(Cl)3-n(SiO2) n], as a new heterogeneous reagent is introduced. This reagent converts alcohols and thiols to their corresponding bromides and iodides in the presence of X2 (X=Br, I) in refluxing CH3CN in high to quantitative yields. Use of Silphos provides a highly practical method for the easy separation of the Silphos oxide byproduct by a simple filtration.
- Iranpoor, Nasser,Firouzabadi, Habib,Jamalian, Arezu,Kazemi, Foad
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p. 5699 - 5704
(2007/10/03)
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- Direct halogenation of alcohols and their derivatives with tert-Butyl halides in the ionic liquid [pmIm]Br under sonication conditions - A novel, efficient and green methodology
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A novel halogenating reagent system for direct halogenation of alcohols has been developed. tert-Butyl bromide, chloride and iodide in combination with the ionic liquid [pmIm]Br have been found to convert alcohols into the corresponding bromides, chlorides and iodides under sonication conditions (or heating) in good yields. Although a variety of primary and secondary alcohols participated in this reaction without any difficulty, tertiary alcohols remained inert. Several alcohol derivatives such as OTMS, OTBDMS, OAc, OTS and OTHP are also transformed into the corresponding halides in one-pot fashion by this procedure. A plausible rationale for this transformation is also presented. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
- Ranu, Brindaban C.,Jana, Ranjan
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p. 755 - 758
(2007/10/03)
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- Fluorous solvent as a new phase-screen medium between reagents and reactants in the bromination and chlorination of alcohols
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(Matrix presented) A perfluorohexane layer regulates the rate of reagent transport in the bromination and chlorination of alcohols. A fluorous triphasic U-tube method is effective for lighter reagents; the thionyl chloride layer (yellow) vanishes, and the chlorides are obtained from the right top organic layer in the chlorination of alcohols.
- Nakamura, Hiroyuki,Usui, Taikou,Kuroda, Hirokazu,Ryu, Ilhyong,Matsubara, Hiroshi,Yasuda, Shinji,Curran, Dennis P.
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p. 1167 - 1169
(2007/10/03)
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- Open-chain dications and betaines with imidazolium molecular motifs: Synthesis and structural aspects
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The synthesis of trinuclear open-chain prototypes gave variable yields: > 53% for dications 1·2X and 2·2X and > 80% for proton-ionizable dications 3·2X-5·2X incorporating 1H-1,2,4-triazole moieties. Deprotonation of the latter compounds resulted in the formation of the betaine counterparts 13·X-15·X. The courses of the dequaternization reactions of compounds 4·2X and 5·2X were also studied. The structural properties of dicationic protophanes 1·2X and 2·2X, containing bis(imidazolium) motifs, were examined by 1H and 13C NMR spectroscopy, electrospray mass spectrometry and by single-crystal X-ray diffraction analysis of the dication 1b·2PF6. Weak noncovalent interactions between the dications and the hexafluorophosphate ions bias the protophane conformation both in solution and in the solid state. X-ray diffraction reveals that the PF6- counterions are located in a channel formed by the dications (1b2+). Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Alcalde, Ermitas,Mesquida, Neus,Alemany, Montserrat,Alvarez-Rua, Carmen,Garcia-Granda, Santiago,Pacheco, Pedro,Perez-Garcia, Lluisa
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p. 1221 - 1231
(2007/10/03)
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- Monomeric bile acid derivatives, processes for their preparation and the use of these compounds as medicaments
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Monomeric bile acid derivatives, processes for their preparation and the use of these compounds as medicaments Monomeric bile acid derivatives of the formula I in which GS, X and Z have the meanings given, and processes for their preparation are described. The compounds have useful pharmacological properties and can therefore be used as medicaments.
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- Benzylphosphonic acid inhibitors of human prostatic acid phosphatase
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A series of α-substituted benzylphosphonic acids is described as inhibitors of human prostatic acid phosphatase, an enzyme has been used as a model to study aryl phosphatases. The most potent inhibitors in this series are 2-trifluoromethylbenzhydrylphosphonic acid (9 μM), and α-(2-phenylethyl)benzylphosphonic acid (14 μM). The structure-activity studies suggest that bulk tolerance beyond the phosphate binding area limits the steric or hydrophobic contribution to inhibitor potency achieved through α-carbon substitution.
- Schwender,Beers,Malloy,Cinicola,Wustrow,Demarest,Jordan
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p. 311 - 314
(2007/10/03)
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- Facile bromination of o-benzylidene sugar and thf ethers with NBS in chloroform in the presence of AIBN
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N-Bromosuccinimide in chloroform in the presence of a catalytic amount of AIBN is found to cleave O-benzylidene sugar into bromobenzoate in efficient manner. THP-ethers were cleaved into bromides and bromo-esters in high yield.
- Raina, Sushil,Srivastava, Kamal K.,Sampath Kumar,Singh, Vinod K.
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p. 121 - 125
(2007/10/03)
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- SOLVOLYSES OF MONOSUBSTITUTED BENZHYDRYL BROMIDES. NUCLEOPHILIC SOLVENT INTERVENTION AND DEPENDENCE OF SOLVATATION ON THE EXTENT OF CHARGE DELOCALIZATION IN CATIONIC TRANSITION STATES
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Solvolyses of monosubstituted benzhydryl bromides gave excellent linear correlations of logk with ?(1+) constants, and not with Y(BnBr) or Y(Br).Correlation analyses against corresponding logk of α-tert-butyl-(2-naphthyl)methyl bromide provided evidence for the importance of different extent of solvation in delocalized transition state and for nucleophilic solvent intervention in the solvolysis of benzhydryl systems.
- Liu, Kwang-Ting,Chin, Chien-Pu,Lin, Yen-Shyi,Tsao, Meng-Lin
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p. 6919 - 6922
(2007/10/02)
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- The Reaction between Acyl Halides and Alcohols: Alkyl Halide vs. Ester Formation
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In the reaction between an acyl halide and an alcohol the thermodynamically favoured products are the free carboxylic acid and the alkyl halide.The initial reaction is, generally, the formation of an ester and HHal.When the alcohol is very prone to yield an alkyl cation upon protonation by HHal, formed H2O exhibited a superior reactivity and competed successfully with the alcohol for the acyl halide making, therefore, ester formation practically confined to a triggering role.But, in those cases where the cation is less easily formed, ester formation was favoured and, consequently, became the necessary elementary step towards alkyl halide formation.Tis final product, on the other hand, might be extremely slow to form in an SN2 reaction between the protonated ester function and the halide ion.In these instances, therefore, as well as in the cases when a basic solvent competes for the proton of HHal, the ester is the final product.A notable exception of the situation above outlined, is given by α-hydroxy-α-phenylbenzeneacetic acid (2y), which appears to undergo direct chlorine-hydroxyl interchange through a quaternary intermediate (E), in the end collapsing to α-chloro-α-phenyl-benzeneacetic acid (4y).Different systems were compared using CH2Cl2 as a solvent under strictly similar conditions.Some 28 different substrates were tested for reaction with AcCl (1a), whereas the action of eight acyl halides (a) against (RS)-α-methylbenzenemethanol (2n) and α-phenylbenzenemethanol (2p), as well as the effect of five different solvents on the reaction between two alcohols (2p and 2-methyl-2-propanol, 2c) with 1a, were observed.
- Strazzolini, Paolo,Giumanini, Angelo G.,Verardo, Giancarlo
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p. 217 - 254
(2007/10/02)
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- Kinetics of the reactions of laser-flash photolytically generated carbenium ions with alkyl and silyl enol ethers. Comparison with the reactivity toward alkenes, allylsilanes and alcohols
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Diarylcarbenium ions (benzhydryl cations) are generated from diarylmethyl chlorides by 20-ns laser pulses (248 nm) in acetonitrile solution at 20°C. The second-order rate constants for their reactions with n- and π-nucleophiles (anions, alcohols, water, alkenes, allylsilanes, alkyl and silyl enol ethers) are determined by monitoring the decay of the UV-vis transients at variable nueleophile concentrations. Only reactive nucleophiles (k2 > 106-107 L mol-1 s-1) can be investigated by this method because of the concomitant reactions of the carbenium ions with the solvent acetonitrile and the chloride ions in produced in the photoheterolysis. The largest observed values of k2 are ～2 × 1010 for reactions with anions and (2-4) × 109 L mol-1 s-1 for reactions with neutral nucleophiles. Alkoxy-substituted ethylenes are 300-105 times more reactive than the corresponding alkyl-substituted ethylenes. The reactivities of structurally analogous alkyl and silyl enol ethers differ by less than 1 order of magnitude. In sharp contrast to the situation previously observed for the reactions of benzhydryl cations with alkenes, the nucleophilic reactivities of the enol ethers correlate with their ionization potentials and not with the stabilities of the carbenium ions produced in the rate-determining step. The rate constants measured for the reactions of the flash photolytically generated benzhydryl cations with alkenes and allylsilanes agree well with those extrapolated from the reactivities of these nucleophiles toward less electrophilic benzhydryl cations, which have previously been determined by conventional techniques. Combination of the two sets of data yields a nucleophilicity scale with respect to the reference electrophile (p-H3CC6H4)2CH+.
- Bartl, J?rg,Steenken, Steen,Mayr, Herbert
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p. 7710 - 7716
(2007/10/02)
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- A Simple Method for the Conversions of Adamantyl, Benzyl and Benzhydryl Alcohols to Their Corresponding Bromides and Chlorides and the Transhalogenation of Adamantyl, Benzyl, Benzhydryl and tertiary Alkyl Bromides and Chlorides
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Adamantyl, benzyl, and benzhydryl alcohols have been converted to their corresponding bromides and chlorides in the absence of a solvent, rapidly and in high yield using boron tribromide and tin(IV) chloride, respectively.Additionally the above bromides and chlorides can be interconverted by a transhalogenation process using the same reagents in the absence of solvent.
- Amrollah-Madjdabadi, A.,Pham, Tung N.,Ashby, E. C.
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p. 614 - 616
(2007/10/02)
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- Elimination Reactions of Alkanesulfenyl Derivatives: Effect of Structure on Reactivity in Thioketone-Forming Eliminations of Diarylmethyl Thiosulfonates
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The reaction of a group of diarylmethyl arenethiosulfonates, ArAr'CHSSO2Ar'' (2), with (a) two alkoxide ions (i-PrO- and MeO-), (b) a series of secondary and tertiary amines of differing base strength, and (c) phenoxide ion has been examined.For each system both the overall rate of disappearance of 2 and the fraction (αelim) converted to thioketone were determined.Salient results are as follows: (1) The ρ values for thioketone-forming elimination of ArAr'CHSSO2C6H4CH3-p with either isopropoxide (+3.4) or piperidine (+3.5) are large and positive, while theρ value associated with variation of the substituent in Ar'' in the elimination of Ph2CHSSO2Ar'' with i-PrO- is quite modest (+1.3). (2) The Broensted β for the elimination reaction of p-nitrobenzhydryl p-toluenethiosulfonate with the series of amines is close to +1.0. (3) While plots of the elimination rate constant (kelim) vs. for any of the amine-induced elimination in amine-amineH+ buffers are linear, plots of kelim vs. -> for the phenoxide-induced elimination in PhO--PhOH buffers very pronounced downward curvature (Figure 4).These various results can be explained by assuming that the different eliminations proceed by different variants of an ElcB mechanism: for the elimination involving amines and 2 a reversible (ElcB)ion pr mechanism (eq 13) is suggested; in the elimination with phenoxide ion the reaction proceeds by an ordinary (ElcB)reversible mechanism (eq 9, ki>kii); in the elimination involving isopropoxide the mechanism becomes (ElcB)irreversible (eq 9, k-iii).Comparison of selected data on the rates of thioketone-forming eliminations of 2 with amines with data obtained previously (ref 6) on the rates of sulfene-forming eliminations of aralkyl α-disulfones with amines indicates that an arylalkanesulfonyl compound undergoes elimination approximately 300 million times faster than the equivalently substituted arylalkanesulfenyl derivative.
- Kice, John L.,Weclas, Ludmilla
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- NOVEL BROMINATION REAGENTS. HEXABROMOCYCLOPENTADIENE: BROMINATION OF ACTIVATED SATURATED SITES
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Hexabromocyclopentadiene (HBC) readily brominates α-keto and benzylic sites, apparently by bromonium ion transfer.
- Magen, Shulamit,Oren, Jakob,Fuchs, Benzion
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p. 3369 - 3372
(2007/10/02)
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- Synthesis of 1-Aminoalkane Phosphonic Acids via Benzhydrylic Schiff Bases
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A simple synthesis of 1-aminoalkanephosphonic acids is described.The addition of diethylphosphite to alkylidene- and arylidenebenzhydrylamines yields the N-benzhydryl-1-aminoalkanephosphonic acid esters.The title compounds are formed by treatment of the N-blocked esters with hydrobromic acid.The starting amine can be recycled from the hydrylbromide. - Key words: 1-Aminoalkane Phosphonic Acids, Benzhydrylic, Schiff Bases
- Issleib, Kurt,Doepfer, Klaus-Peter,Balszuweit, Arno
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p. 1392 - 1394
(2007/10/02)
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- Carbon-Halogen Bonding Studies. Halogen Redistribution Reactions between Alkyl or Acetyl Halides and Tri-n-butyltin Halides
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The equilibrium positions have been determined for the halogen redistribution reactions of tri-n-butyltin halides with a variety of structurally different types of alkyl halides and with acetyl halides.These have been related through the reaction ΔGo values to carbon-halogen bond dissociation energy differences.It is suggested that the trends observed in the latter may provide evidence for the existence of a small steric bond weakening effect in the order C-I > C-Br > C-Cl bonds on going from methyl to primary, secondary, and tertiary alkyl halides.On the other hand, with the 2,3-? bond containing allyl, benzyl, and propargyl halides , α-haloacetones, and haloacetonitriles, there may be some type of electronic carbon-halogen bond strengthening effect which lies in order C-I > C-Br > C-Cl.Finally, for the acetyl halides, the data are in agreement with increases in bond strengths resulting from ? contributions being in the order C-Cl > C-Br > C-I.
- Friedrich, Edwin C.,Abma, Charles B.
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p. 1367 - 1371
(2007/10/02)
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