- Two ways of spin crossover in an iron(ii) coordination polymer associated with conformational changes of a bridging ligand
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1,4-Di(1-ethyl-1,2,3-triazol-5-yl)butane (bbtre) was prepared by lithiation of 1-ethyl-1,2,3-triazole, followed by alkylation with 1,4-dibromobutane. The ligand bbtre forms a three-dimensional network with Fe(ii), [Fe(bbtre)3](ClO4)2·2CH3CN, that exhibits thermally induced spin crossover (SCO). A change of temperature or change of spin state results in various types of structural transformation, leading to different structures that are stable in strictly defined temperature ranges. As a result, there are three spin crossover transitions arranged via two different paths. Thus, cooling below 280 K involves a HT(HS) → LT(HS) (HT, high temperature structure; LT, low temperature structure; HS, high spin) phase transition (PT), which is associated with conformational changes of the bbtre molecules and with deformation of the polymeric skeleton. In the LT phase incomplete and reversible LT(HS) ? LT(HS/LS) spin crossover occurs (LS, low spin). In contrast, rapid cooling (of a sample not previously thermally treated) allows the HT(HS) → LT(HS) phase transition to be avoided, and so complete HT(HS) → HT1(LS) SCO occurs. This means that the PT plays the role of a switch, which allows a choice of one of two ways in which the SCO will proceed. After rapid cooling, further heating to 150 K and subsequent cooling results in a reversible HT1(HS) ? HT1(LS) spin crossover (T↓1/2 = 130 K, T↑1/2 = 131 K). However, raising the temperature to 170-200 K leads to formation of a modulated structure HT2(HS) exhibiting the next reversible HT2(HS) ? HT2(LS) SCO (T↓1/2 = 121 K, T↑1/2 = 123 K). Finally, heating above 200 K involves the HT2(HS) → LT(HS) PT and results in a LT(HS) structure exhibiting incomplete LT(HS) ? LT(HS/LS) spin crossover.
- Ksi??ek, Maria,Weselski, Marek,Dreczko, Agnieszka,Maliuzhenko, Vladyslav,Ka?mierczak, Marcin,To?oczko, Aleksandra,Kusz, Joachim,Bronisz, Robert
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p. 9811 - 9819
(2020/07/30)
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- THIAZOLE DERIVATIVES AS METALLO-BETA-LACTAMASE INHIBITORS
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A compound which is a thiazole derivative of Formula (I), or a pharmaceutically acceptable salt thereof, wherein R1, R2, n, Z, L, Ring B, R4 and n are as herein defined. Such compounds are useful in the prevention and trea
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Paragraph 0235-0236
(2019/12/08)
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- Taming Ambident Triazole Anions: Regioselective Ion Pairing Catalyzes Direct N-Alkylation with Atypical Regioselectivity
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Controlling the regioselectivity of ambident nucleophiles toward alkylating agents is a fundamental problem in heterocyclic chemistry. Unsubstituted triazoles are particularly challenging, often requiring inefficient stepwise protection-deprotection strategies and prefunctionalization protocols. Herein we report on the alkylation of archetypal ambident 1,2,4-triazole, 1,2,3-triazole, and their anions, analyzed by in situ 1H/19F NMR, kinetic modeling, diffusion-ordered NMR spectroscopy, X-ray crystallography, highly correlated coupled-cluster computations [CCSD(T)-F12, DF-LCCSD(T)-F12, DLPNO-CCSD(T)], and Marcus theory. The resulting mechanistic insights allow design of an organocatalytic methodology for ambident control in the direct N-alkylation of unsubstituted triazole anions. Amidinium and guanidinium receptors are shown to act as strongly coordinating phase-transfer organocatalysts, shuttling triazolate anions into solution. The intimate ion pairs formed in solution retain the reactivity of liberated triazole anions but, by virtue of highly regioselective ion pairing, exhibit alkylation selectivities that are completely inverted (1,2,4-triazole) or substantially enhanced (1,2,3-triazole) compared to the parent anions. The methodology allows direct access to 4-alkyl-1,2,4-triazoles (rr up to 94:6) and 1-alkyl-1,2,3-triazoles (rr up to 99:1) in one step. Regioselective ion pairing acts in effect as a noncovalent in situ protection mechanism, a concept that may have broader application in the control of ambident systems.
- Dale, Harvey J.A.,Hodges, George R.,Lloyd-Jones, Guy C.
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supporting information
p. 7181 - 7193
(2019/05/10)
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- Perfluorinated 1,2,3- and 1,2,4-Triazolium Ionic Liquids
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Dialkyl triazolium triflimides with perfluorinated side chains were prepared as hydrophobic ionic liquids (ILs) for surface impregnation. The key feature of the new materials are relatively short perfluorohexyl residues (nC6F13 = RF) as the fluorinated part of the cations, making the target compounds beneficial alternatives to established products because of their enhanced degradability and therefore lower bioaccumulativity. As heterocyclic scaffold, either 1,2,3-triazole or 1,2,4-triazole were chosen. As the two alkyl moieties, either two RFCH2CH2 groups or one RFCH2CH2 and one Et residue were applied. The diethyl congeners were also prepared. Fluorinated starting materials were RFCH2CH2OTf as alkylating reagent or RFCH2CH2N3 as 1,3-dipole for a copper catalyzed cycloaddition (CuAAC) with trimethylsilyl acetylene. After sequential CuAAC and alkylation reactions, the triflimide salts were finally obtained from the intermediate iodides or triflates with the aid of an ion exchange resin. Out of 14 triazolium salts prepared, four compounds have finally been identified as hydrophobic ILs (contact angles between 85° and 100° with mp. 100 °C), being promising materials for surface impregnation: the 1,2,3-triazolium triflate and triflimide with two fluorinated alkyl residues, and the 1,2,4-triazolium triflimides (two regioisomers) with one fluorinated alkyl residues and one ethyl group.
- Alpers, Torben,Muesmann, Thomas W. T.,Temme, Oliver,Christoffers, Jens
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p. 4331 - 4337
(2018/08/31)
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- General solution to the synthesis of N-2-substituted 1,2,3-triazoles
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The regioselective N-alkylation of 1,2,3-triazoles 1 - 6 was studied. Good to excellent N-2 selectivity and high chemical yields for N-2-substituted 4,5-dibromotriazoles 7 were obtained with 4,5-dibromo- and 4-bromo-5- trimethylsilyl-1,2,3-triazoles. These building blocks can be readily converted to 2-mono-, 2,4-di-, and 2,4,5-polysubstituted triazoles 10 - 15, providing a general, protective, group-free method for the synthesis of N-2-substituted triazoles. Observed regioselectivities can be rationalized by a combination of Frontier Molecular Orbital, steric, and electrostatic directing effects on the heterocyclic scaffolds.
- Wang, Xiao-Jun,Zhang, Li,Krishnamurthy, Dhileepkumar,Senanayake, Chris H.,Wipf, Peter
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scheme or table
p. 4632 - 4635
(2010/12/18)
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- Alkylation and acylation of the 1,2,3,triazole ring
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Trimethylsilylation of 1,2,3-triazole regioselectively proceeded to give 2-trimethylsilyl-2H-1,2,3-triazole, which was treated with primary alkyl halides in the presence of tetrabutylammonium fluoride to give 1-alkyl-1H- 1,2,3-triazoles as a Sole product 1-Methyl-5-substituted 1H-1,2,3-triazoles were prepared by alkylation of 5-lithio-1-methyl-1H-1,2,3-triazole, and 1- methyl-4-substituted 1H-1,2,3-triazoles were obtained by alkylation of 4- lithio-1-methyl-5-phenylthio-1H-1,2,3-triazole followed by reductive desulfurization.
- Ohta, Shunsaku,Kawasaki, Ikuo,Uemura, Takahiro,Yamashita, Masayuki,Yoshioka, Tomomichi,Yamaguchi, Satoshi
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p. 1140 - 1145
(2007/10/03)
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- SYNTHESIS OF POLYNUCLEAR UNCONDENSED TRI- AND TETRAZOLES
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A number of the corresponding 1- and 2-propargylazoles were obtained by propargylation of 5-substituted tetrazoles and 1,2,3-triazoles with various degrees of substitution.Polyazole structures with a system of two to five uncondensed azole rings were synthesized by the reaction of the 1- and 2-propargylazoles with organic azides, diazides, and azoles, as well as by oxidative dimerization.
- Vereshchagin, L. I.,Maksikova, A. V.,Tikhonova, L. G.,Buzilova, S. R.,Sakovich, G. V.
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p. 510 - 515
(2007/10/02)
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