109975-61-3Relevant articles and documents
Electrophilic activation of acetyl-substituted heteroaromatic compounds
Klumpp,Garza,Sanchez Jr.,Lau,De Leon
, p. 8997 - 9000 (2000)
The chemistry of acetyl-substituted pyridines, thiazoles, quinoline, isoquinolines, and pyrazine (1-9 and 28) has been studied. These heteroarenes (1-8) condense with benzene in good yields (74-96%) in the Bronsted superacid, CF3SO3H (triflic acid). In these acid-catalyzed hydroxyalkylation reactions, compounds 1-8 are significantly more reactive than acetophenone. It is proposed that compounds 1-8 readily form dicationic electrophiles in triflic acid.
Lewis Acid-Catalyzed Selective Reductive Decarboxylative Pyridylation of N-Hydroxyphthalimide Esters: Synthesis of Congested Pyridine-Substituted Quaternary Carbons
Gao, Liuzhou,Wang, Guoqiang,Cao, Jia,Chen, Hui,Gu, Yuming,Liu, Xueting,Cheng, Xu,Ma, Jing,Li, Shuhua
, p. 10142 - 10151 (2019/10/16)
A practical and efficient Lewis acid-catalyzed radical-radical coupling reaction of N-hydroxyphthalimide esters and 4-cyanopyridines with inexpensive bis(pinacolato)diboron as reductant has been developed. With ZnCl2 as the catalyst, a wide range of quaternary 4-substituted pyridines, including highly congested diarylmethyl and triarylmethyl substituents, could be selectively obtained in moderate to good yields with broad functional group tolerance. Combined theoretical calculations and experimental studies indicate that the Lewis acid could coordinate with the cyano group of the pyridine-boryl radical to lower the activation barrier of the C-C coupling pathway, leading to the formation of 4-substituted pyridines. Moreover, it could also facilitate the decyanation/aromatization of the radical-radical coupling intermediate.
Carbon-Skeletal Anionic and Radical Sigmatropic Rearrangements: Group Migratory Aptitudes as a Probe of Charge Type in the 1,2-Shifts of β-Phenyl-β-(2-pyridyl)- and β-Phenyl-β-(4-pyridyl)ethyl Systems
Eisch, John J.,Kovacs, Csaba A.,Chobe, Prabodh,Boleslawski, Marek P.
, p. 4427 - 4437 (2007/10/02)
In order to probe the occurrence and relative ease of carbon-skeletal sigmatropic rearrangements of the free-radical, anionic, or radical-anionic type, derivatives of the β,β-diphenyl-β-(2-pyridyl)- and the β,β-diphenyl-β-(4-pyridyl)ethane systems, PyPh2CCH2E (A), were treated with reagents expected to generate radical or anionic sites.The ensuing, competitive -shifts of the phenyl and/or pyridyl groups were then used as a diagnostic sign of the mechanism of rearrangement.Both the treatment of A (E = p-tolyl) with MeLi or KH and the reaction of A (E = Cl) with sodium or lithium in donor solvents caused an exclusive -pyridyl shift.Gas chromatographic and mass spectral analyses were able to place the limit of any -phenyl shift as under 0.5percent.In such alkali metal reactions, persistent aromatic radical-anions were detected by ESR spectroscopy until the completion of the reaction.Such signals and the significant amounts of carbon-carbon bond cleavage products support the formation of pyridyl radical-anions as precursors for such cleavages and -pyridyl rearrangements.That such radical-anions could lead to spiro intermediates that promote the -pyridyl migrations wins corroboration from the finding that the methiodide of 1-chloro-2-methyl-2-(4-pyridyl)propane can be reduced with lithium in THF to yield the isolable 1,1,6-trimethyl-6-azaspiroocta-4,7-diene.The same two chlorides of A responded differently under other rearrangement conditions: (1) in preparing such chlorides from the corresponding alcohols, PyPh2CCH2OH, with thionyl chloride, the 4-pyridyl isomer underwent a Wagner-Meerwein rearrangement with exclusive -phenyl migration; the 2 isomer underwent normal displacement of OH by Cl; (2) toward the free-radical reducing agent, (n-Bu)3SnH, the 2-chloro isomer underwent both -phenyl and -pyridyl shifts, while the 4-chloro isomer underwent neither reduction nor rearrangement; it simply induced the formation of hexa-n-butylditin.A similar reducing action was observed with bis(1,5-cyclooctadiene)nickel.These observations are analyzed with the aid of Hueckel molecular orbital theory and the rearrangements observed with reducing agents are assessed in terms of three types of mechanisms: (1) authentic -anionic shifts; (2) authentic -free-radical shifts; and (3) competing electron transfer from the metal to the chloride center or from the metal to the pyridyl ring, which permits anionic rearrangements to compete with rearrangements mediated by radical-anion or dianions, which latter processes form the crucial spiro intermediate by intramolecular nucleophilic displacement on the CH2Cl group.
