Enhancement of Benzylic basicity by a fluorine substituent at the para- position: a case of lone pair/lone pair repulsion

Détails

ID Serval
serval:BIB_17714
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Institution
Titre
Enhancement of Benzylic basicity by a fluorine substituent at the para- position: a case of lone pair/lone pair repulsion
Périodique
Chemistry (weinheim An Der Bergstrasse, Germany)
Auteur⸱e⸱s
Faigl F., Marzi E., Schlosser M.
ISSN
1521-3765 (Electronic)
ISSN-L
0947-6539
Statut éditorial
Publié
Date de publication
2000
Volume
6
Numéro
5
Pages
771-777
Notes
Publication types: JOURNAL ARTICLE
Publication Status: ppublish
Résumé
The introduction of a halogen atom at any aromatic position of toluene considerably accelerates the base-promoted deprotonation of the methyl group. p-Fluorotoluene is the only exception; proton abstraction from its benzylic site occurs approximately at one tenth of the rate found with toluene (at -75 degrees C). Lone-pair repulsion appears to be at the origin of the decrease in acidity. Chloro- and bromotoluenes instantaneously exchange benzylic hydrogen against metal when treated with solution of lithium 2,2,6,6-tetramethylpiperidide (LITMP) in diethyl ether in the presence of potassium tert-butoxide and N,N,N',N",N"-pentamethyldiethylenetriamine at -100 degrees C. Due to extensive side reactions ("aryne" formation as a consequence of concomitant deprotonation of aromatic sites adjacent to the halogen atom), products can be isolated only in moderate yield (10-35%), but they are regioisomerically pure.
Pubmed
Création de la notice
19/11/2007 9:39
Dernière modification de la notice
20/08/2019 12:47
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