The kinetic isotope effects in deuterium and tritium exchange in benzene, fluorobenzene, pyridine, pyridine N-oxide, and quinoline with a solution of an alkali metal amide in liquid ammonia k(D)(NH3)/k(T)(NH3) were determined, where k(D)(NH3) and k(T)(NH3) are the experimental rate constants of protodedeuteration and protodetritiation, respectively. The variation of the tritium exchange rates in benzene in going from NH3 to ND3 (k(T)(NH3) and k(T)(ND3)) was evaluated. The deviation of the observed ratios k(D)(NH3)/k(T)(NH3) and k(H)(ND3)/k(T)(ND3) from the maximum possible values corresponding to the Swan-Shaad equation suggests the reaction mechanism in which both elementary stages, ionization of the CH acid and diffusion separation of the complex of the carbanion with the ammonia molecule, are partially limiting. A small decrease in the secondary isotope effect of the solvent, defined as k(T)(ND3)/k(T)(NH3) as compared to the theoretical maximum of 2.4, is assumed to be due to similar structures of the transition state and the equilibrium carbanion. A theoretical explanation was given for the observed dependences of the primary isotope effect of the substrate on pK(a) for deutero (tritio) derivatives of fluorobenzene [4D(t) < 3D(t) < 2D(t)], for reactions in the series pyridine-2D(t) < pyridine-3D(t) < quinoline3D(t), and for hydrogen exchange in pyridine-2D(t) N-oxide (k(D)(NH3)/k(T)(NH3) similar to 1).
Functionalization of pyridine via direct metallation
作者:Jacob Verbeek、Albert V. E. George、Robertus L. P. de Jong、Lambert Brandsma
DOI:10.1039/c39840000257
日期:——
The isolation of mixtures of 2-, 3-, and 4-deuteriopyridine, 2-, 3-, and 4-trimethylsilylpyridine, or 2-, 3-, and 4-methylthiopyridine indicates successful metallation of pyridine with a 1 : 1 mixture of BuLi-ButOK in tetrahydrofuran–hexane at ––100 °C.
2-,3-和4-氘代吡啶,2-,3-和4-三甲基甲硅烷基吡啶或2-,3-和4-甲硫基吡啶的混合物的分离表明,吡啶与1:1的混合物成功地金属化在––100°C下于四氢呋喃–己烷中的BuLi-Bu t OK。
Position-Specific Secondary Deuterium Isotope Effects on Basicity of Pyridine
作者:Charles L. Perrin、Phaneendrasai Karri
DOI:10.1021/ja105331g
日期:2010.9.1
Secondaryisotopeeffects (IEs) on basicities of various deuterated pyridine isotopologues and of 2,6-lutidine-2,6-(CD(3))(2) have been accurately measured in aqueous solution by an NMR titration method applicable to a mixture. Deuteration at any position of pyridine increases the basicity, but the IE per deuterium is largest for substitution at the 3-position and smallest for the 2-position, which
activator for carboxylic acids is the key to bypass a competing single‐electron‐transfer mechanism and “switch on” an energy‐transfer‐mediated homolysis of unsymmetrical σ‐bonds for a concertedfragmentation/decarboxylation process.
Unusual<i>t</i>-BuLi Induced Ortholithiation versus Halogen-Lithium Exchange in Bromopyridines: Two Alternative Strategies for Functionalization
作者:Philippe Gros、Yves Fort、Philippe Pierrat
DOI:10.1055/s-2004-831337
日期:——
The reaction of lithiating agents with various 3-bromopyridines has been investigated. An unprecedented selectivity was observed with t-BuLi, which effected a clean lithiation at C-4. With 3-bromo and 2-chloro-3-bromo pyridines, the ortholithiation-exchange ratio was strongly electrophile and addition order dependent while 2-chloro-5-bromopyridine always gave exclusive C-4 substitution.
Reactions of nitrogen containing aromatic anions with chlorocarbene
作者:U. Burger、F. Dreier
DOI:10.1016/s0040-4020(01)91924-6
日期:1983.1
ring fission upon reaction with chlorocarbene in tetrahydrofuran. Acetylenes (12 and 18) are the result. The reaction of 1 is accompanied by ring enlargement to indolizine (7). When the reaction of 1 with chlorocarbene is performed in diethylether, again 7 is produced, this time accompanied by a tetracyclic valence isomer, the pyrroloazabenzvalene (8). Mechanistic implications, based on the finding