Reactions of N-chlorobenzylmethylamines with secondary amines in acetonitrile. Effect of base strength upon the imine-forming transition state

1986 ◽  
Vol 51 (8) ◽  
pp. 1320-1324 ◽  
Author(s):  
Bong Rae Cho ◽  
Sung Keon Namgoong ◽  
Richard A. Bartsch
Keyword(s):  
Transition State ◽  
Secondary Amines ◽  
Base Strength

Medium effect (water versus MeCN) on reactivity and reaction pathways for the SNAr reaction of 1-aryloxy-2,4-dinitrobenzenes with cyclic secondary amines

2017 ◽  
Vol 95 (12) ◽  
pp. 1273-1279 ◽  
Author(s):  
Ik-Hwan Um ◽  
Min-Young Kim ◽  
Julian M. Dust
Keyword(s):  
Transition State ◽  
Secondary Amines ◽  
Medium Effect ◽  
Strong Electron ◽  
Cyclic Transition ◽  
Cyclic Transition State ◽  
Snar Reaction ◽  
Electron Withdrawing Group ◽  
Catalyzed Reactions ◽  
Zwitterionic Intermediate

A kinetic study on SNAr reactions of 1-aryloxy-2,4-dinitrobenzenes (1a–1h) with a series of cyclic secondary amines in 80 mol% water – 20 mol% DMSO at 25.0 ± 0.1 °C is reported. The plots of kobsd versus amine concentration curve upward except for the reactions of substrates possessing a strong electron-withdrawing group in the leaving aryloxide with strongly basic piperidine. The curved plots indicate that the reactions proceed through both uncatalytic and catalytic routes. Linear Brønsted-type plots have been obtained for the uncatalyzed and catalyzed reactions of 1-(4-nitrophenoxy)-2,4-dinitrobenzene (1a) with βnuc = 0.84 and 0.78, respectively. The Yukawa–Tsuno plot for the uncatalyzed reactions of 1a–1h with piperidine results in an excellent linear correlation with ρ = 1.66 and r = 0.31. In contrast, rate constants for catalyzed reactions are independent of the electronic nature of the substituent in the leaving group. The current SNAr reactions have been proposed to proceed via a zwitterionic intermediate (MC±) that partitions to products through uncatalytic and catalytic routes. The catalyzed reaction from MC± has been concluded to proceed through a concerted mechanism with a six-membered cyclic transition state (TScycl) rather than via a stepwise pathway with a discrete anionic intermediate (MC−), the traditionally accepted mechanism. Medium effects on the reactivity and reaction mechanism are discussed. Particularly, hydrogen bonding of the amines to water precludes formation of kinetically significant dimers found in some aprotic solvents; no explicit role for water in the catalytic transition state is required or proposed. The specific stabilization of the leaving aryloxides substituted with strong electron-withdrawing groups accounts for the lack of the catalytic pathway in these systems (1a–1c) with piperidine nucleophile.

scholarly journals A CO2-Catalyzed Transamidation Reaction

2020 ◽  
Author(s):  
Yang Yang ◽  
Jian Liu ◽  
JIWOONG LEE
Keyword(s):  
Transition State ◽  
Bond Formation ◽  
Metal Catalysts ◽  
Amide Bond ◽  
Secondary Amines ◽  
Coupling Reagents ◽  
Reaction Conditions ◽  
Amide Bond Formation ◽  
Primary And Secondary Amines ◽  
Bond Formation Reactions

<div> <div> <div> <p>Amide bond formation reactions are often mediated by reactive substrates in the presence of over-stoichiometric activating reagents and/or catalysts. Here we report a CO2-promoted transamidation reaction without additive metal catalysts or coupling reagents. The reaction forms byproducts, ammonia, primary and secondary amines, which can form adducts with CO2, thereby shifting the equilibrium in the desired direction. A comparison of Hammett studies under CO2 and N2 atmospheres suggests that the reaction transition state can be stabilized by electrophilic CO2. Selective modification of peptides was demonstrated, showing that CO2 can be utilized to control the nature of the electrophilicity and nucleophilicity of reaction partners under practical reaction conditions. </p> </div> </div> </div>

scholarly journals A CO2-Catalyzed Transamidation Reaction

2020 ◽  
Author(s):  
Yang Yang ◽  
Jian Liu ◽  
JIWOONG LEE
Keyword(s):  
Transition State ◽  
Bond Formation ◽  
Metal Catalysts ◽  
Amide Bond ◽  
Secondary Amines ◽  
Coupling Reagents ◽  
Reaction Conditions ◽  
Amide Bond Formation ◽  
Primary And Secondary Amines ◽  
Bond Formation Reactions

<div> <div> <div> <p>Amide bond formation reactions are often mediated by reactive substrates in the presence of over-stoichiometric activating reagents and/or catalysts. Here we report a CO2-promoted transamidation reaction without additive metal catalysts or coupling reagents. The reaction forms byproducts, ammonia, primary and secondary amines, which can form adducts with CO2, thereby shifting the equilibrium in the desired direction. A comparison of Hammett studies under CO2 and N2 atmospheres suggests that the reaction transition state can be stabilized by electrophilic CO2. Selective modification of peptides was demonstrated, showing that CO2 can be utilized to control the nature of the electrophilicity and nucleophilicity of reaction partners under practical reaction conditions. </p> </div> </div> </div>

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