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Fluorine‐Flanked Congested Sites: Minimal, Though Perceptible Buttressing Effects on the Proton Mobility of Arenes
Author(s) -
Heiss Christophe,
Leroux Frédéric,
Schlosser Manfred
Publication year - 2005
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200500552
Subject(s) - chemistry , triethylsilane , trimethylsilane , metalation , deprotonation , medicinal chemistry , substituent , steric effects , halogen , fluorine , stereochemistry , aryne , transmetalation , organic chemistry , ion , alkyl , catalysis
(2,6‐Difluorophenyl)trimethylsilane, ‐triethylsilane and ‐triisopropylsilane undergo sec ‐butyllithium‐mediated metalation at the 3‐ and 4‐position ( ortho and meta relative to the halogen) in ratios of 99.6:0.4, 98:2 and 95:5, respectively. The steric pressure transmitted by the fluorine atoms can be increased if the trialkylsilyl group is locked up on the other side by a relatively voluminous substituent. Whereas (2,6‐difluorophenyl)triethylsilane is attacked by lithium 2,2,6,6‐tetramethylpiperidide under deprotonation of the 4‐ and 5‐position in a ratio of 99.4:0.6, the proportion of “ ortho ”/“ meta ” metalation changes to 84:16 when (2‐bromo‐6‐fluorophenyl)triethylsilane acts as the substrate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)