Fluorine‐Flanked Congested Sites: Minimal, Though Perceptible Buttressing Effects on the Proton Mobility of Arenes

(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)