2767-91-1Relevant academic research and scientific papers
Structures, Lewis Acidities, Electrophilicities, and Protecting Group Abilities of Phenylfluorenylium and Tritylium Ions
Follet, Elsa,Mayer, Peter,Berionni, Guillaume
supporting information, p. 623 - 630 (2017/01/18)
The isolation, characterization, and the first X-ray structures of a fluorenylium ion and its Lewis adducts with nitrogen- and phosphorus-centered Lewis bases are reported. Kinetics of the reactions of a series of fluorenylium ions with reference π-, σ-, and n-nucleophiles of various sizes and nucleophilicities allowed the interplay between electronic and structural parameters on the electrophilicities of these planarized tertiary carbenium ions to be elucidated. Structure–reactivity correlations and extensive comparisons of their reactivities with those of di- and triarylcarbenium ions are described. Quantitative determination of the electrofugalities of fluorenylium ions revealed to which extent they are complementing tritylium ions as protecting groups and how their tuning is possible. Determination of the equilibrium constants of the Lewis adducts formation between pyridines of calibrated Lewis basicities and phenylfluorenylium and tritylium ions allowed the determination of their Lewis acidities and to showcase the potential of these carbon-centered Lewis acids in catalysis.
The Rate and Equilibrium Constants for N-, O-Acyl Transfer
Rybachenko,Chotii,Kovalenko,Shreder
, p. 1695 - 1698 (2007/10/03)
Reactions with dimethylcarbamoyl group transfer from N-acylpyridinium salts to pyridine N-oxides and from N-acyloxypyridinium salts to pyridines in acetonirile solutions were studied. Their rate and equilibrium constants and activation parameters were determined. The reactions were shown to be one-step and to follow the SN2 mechanism. Equations relating the rate and equilibrium parameters of the N-O and O-N acyl transfer reactions to the basicity of the nucleophile and outgoing group were obtained.
Some reactions of pyridinium salts derived from trichloromethylarenes with N- and C-nucleophiles
Belen'kii,Poddubnyi,Luiksaar,Krayushkin
, p. 1172 - 1176 (2007/10/03)
The reaction of N-(4-pyridyl)pyridinium and 4-chloropyridinium salts obtained from 1-trichloromethyl-2,4,6-trimethylbenzene and pyridine with N-nucleophiles such as piperidine and morpholine and with C-nucleophiles such as N,N-dimethylaniline and indole proceeds through hetarylation and gives the corresponding 4-substituted pyridines. N-(α,α-Dichlorobenzyl)pyridinium and N,N'-(α-chlorobenzylidene)bispyridinium salts obtained from trichloromethylbenzene do not undergo hetarylation.
Rate-Determining Steps in Michael-Type Additions and E1cb Reactions in Aqueous Solution
Heo, Christina K. M.,Bunting, John W.
, p. 3570 - 3578 (2007/10/02)
Rates of equilibration of a series of 10 substituted pyridines and five Michael acceptors (CH2=CHZ, Z = CHO, COCH3, SO2CH3, CN and CONH2) with the corresponding N(ZCH2CH2) pyridinium cations have been measured in aqueous solution at ionic strength 0.1 and 25 deg C.Analysis of the dependence of the pseudo-first-order rate constants for equilibration as a function of acceptor concentration and of pH allows the evaluation of the second-order rate constants (kNu) for the nucleophilic attack of each of these pyridines upon each of these acceptors and also the second-order rate constants (kOH) for the hydroxide ion catalyzed E1cb elimination reaction which is the microscopic reverse of each of these Michael-type addition reactions.Broensted-type plots for each of these processes as a function of the basicity of the substituted pyridine are concave down for each of Z = CHO, COCH3, and CN and are consistent with a change from rate-determining nucleophilic attack for the more basic pyridines to rate-determining protonation of the carbanionic intermediate by a water molecule for less basic pyridines and the corresponding microscopic reverse processes in the elimination reactions.The "break" in these Broensted-type plots is shown to occur at a pyridine basicity that is a function of the Z-activating substituent.Broensted β1g and βnuc are evaluated for each rate-determining step (wherever accessible); these two parameters are shown to pass through minima as a function of reactivity. βeq is shown to be a simple linear function of reactivity (as log kNu) for nucleophilic addition to the acceptor species, although Keq is relatively insensitive to the nature of the Z-activating substituent.
Photochemical Induced Formation of α-Alkylamino or Alkylaminyl Radicals From Secondary Amines: Reaction with 4-Pyridinecarbonitrile
Caronna, Tullio,Morrocchi, Sergio
, p. 975 - 977 (2007/10/02)
The direct photolysis at 254 nm of 4-pyridinecarbonitrile in the presence of some aliphatic secondary amines brought to the substitution of the CN group and to the formation of 4-α-alkylaminopyridines, whereas the irradiation in the presence of benzophenone at 350 nm yields 4-alkylaminylpyridines and 4-diphenylketylpyridine.A mechanism is proposed to explain the different course of the reaction under the two different conditions.
A Change in the Rate-Determining Step in the E1cB Reactions of N-(2-(4-Nitrophenyl)ethyl)pyridinium Cations
Bunting, John W.,Kanter, James P.
, p. 6950 - 6954 (2007/10/02)
Second-order rate constants have been measured (aqueous solution, I = 1.0, 25 deg C) for the hydroxide ion catalyzed elimination reactions of 12 N-(2-(4-nitrophenyl)ethyl)pyridinium cations (3) bearing a variety of substituents in the pyridine ring.Broensted plots as a function of the basicity of the pyridine leaving group are concave-down, which is consistent with a change in rate-determining step within an E1cB mechanism.These plots are characterized by βlg = -0.17 for the rate-determining deprotonation for pKBH lg = -0.39 for the rate-determining expulsion of the pyridine nucleofuge from the carbanionic intermediate for pKBH > 6.5.Elimination reactions in basic D2O occur without any significant incorporation of deuterium into the 4-nitrostyrene product, and require the presence of a hydrogen-bonded carbanionic intermediate in which nucleofuge expulsion occurs faster than exchange of hydrogen-bonding water molecules.Rate-determining deprotonation in these elimination reactions occurs 50-fold more slowly than for the corresponding reactions of the N-quinuclidinium cations that have also been reported to have βlg = -0.17, but which do not show an analogous change in the rate-determining step upon variation of the nucleofuge basicity.The analogous elimination of the 1-methyl-3-imidazolium cation occurs a further 30-fold more slowly than that predicted for 3 having a pyridine leaving group of the same basicity as 1-methylimidazole.The E1cB reactions of 3 are similar to the analogous reactions of N-(2-cyanoethyl)pyridinium cations (1) in displaying a change in the rate-determining step with nucleofuge basicity; however, theβlg values for 1 and 3 are quite different for both k1 and k2/k-1.
Equilibration of N-(2-cyanoethyl)pyridinium cations with substituted pyridines and acrylonitrile. A change in rate-determining step in an E1cb reaction
Bunting, John W.,Toth, Andrea,Heo, Christina K. M.,Moors, Rodney G.
, p. 8878 - 8885 (2007/10/02)
The rates of equilibration of N-(2-cyanoethyl)pyridinium cations (1) with the corresponding pyridines and acrylonitrile have been measured in aqueous solutions of ionic strength 0.1 at 25 °C. Second-order rate constants (kOH) have been obtained for the hydroxide ion catalyzed elimination reactions of 16 ring-substituted 1 having pyridine leaving groups of pKBH in the range 1.5-9.7. Bronsted plots of log kOH vs pKBH are "concave down" with two distinct linear regions having β1g = -0.30 (for pKBH 1g = -0.93 (for pKBH > 5.8). This observation is consistent with a change in rate-determining step within an E1cb reaction mechanism from rate-determining deprotonation of 1 (i.e., (E1cb)irrev) for pKBH rev) for pKBH > 5.8. This interpretation is supported by 1H NMR spectral observations in basic D2O, which show no incorporation of deuterium into the acrylonitrile product for pKBH BH > 5.8. Rates of nucleophilic attack of pyridines and pyridinone anions (pKBH > 6) upon acrylonitrile have also been measured. These display a linear Br?nsted plot of βnuc = 0.20. Combination of β1g and βnuc gives βeq = 0.13 for the Michael-type addition of pyridinium cations to acrylonitrile to produce 1. Although the rates of the addition of pyridines of pKBH nuc = 0.20 for pyridines of pKBH > 5.8 to rate-determining protonation of the carbanionic intermediate with βnuc = 0.83 for pyridine nucleophiles of pKBH irrev region but is extremely weak under the current experimental conditions.
Process for the preparation of aminopyridines
-
, (2008/06/13)
A process for the preparation of aminopyridines of the formula STR1 wherein R1 and R2 are identical or different and are hydrogen or lower alkyl or, together with the nitrogen atom to which they are attached, form a 5-, 6-, or 7-membered heterocyclic ring containing up to 2 more hetero atoms, comprises reacting 4-pyridylpyridinium chloride or a salt thereof, at an elevated temperature, with an acid amide of the formula STR2 wherein R1 and R2 are as above and Z is --CO--R3 wherein R3 is hydrogen, lower alkyl, STR3 and R4 and R5 are hydrogen or lower alkyl.
