Trifluoromethyl‐Substituted Phenylsilanes: The Regiochemical Course of Their Metalation Dictated by Buttressing Effects

Triethyl[(2‐trifluoromethyl)phenyl]silane reacts with the superbasic LIC‐KOR mixture of butyllithium and potassium tert ‐butoxide exclusively at the 4‐position (“ meta ‐metalation”) and not at all at the 3‐position (“ ortho ‐metalation”). Two further substrates which simultaneously contain two trifluoromethyl groups, triethyl[2,4‐ and 2,5‐bis(trifluoromethyl)phenyl]silane, undergo deprotonation at the 5‐ and 4‐position, respectively. Thus, a buttressing effect blocks the attack of metalating agents on the ortho position of any trifluoromethyl group which is neighbored, on the other side, by a trialkyl substituent. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)