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

Ferenc Faigl, Elena Marzi, Manfred Schlosser

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

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°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-buloxide. and N,N,N′,N″,N″-pentamethyldiethylenetriamine at -100°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.

Original languageEnglish
Pages (from-to)771-777
Number of pages7
JournalChemistry - A European Journal
Volume6
Issue number5
Publication statusPublished - Mar 3 2000

Keywords

  • Acidity
  • Electron-electron repulsion
  • Fluorine
  • Lithiation
  • Substituent effects

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

Fingerprint Dive into the research topics of 'Enhancement of benzylic basicity by a fluorine substituent at the para-position: A case of lone pair/lone pair repulsion'. Together they form a unique fingerprint.

  • Cite this