Fluorine- and trifluoromethyl-substituted toluenes: site selective metalation of aromatic or benzylic positions

At -75 Deg, the superbasic mixt. of BuLi and KOCMe3 metalates 2-, 3-, and 4-FC6H4Me exclusively at an arom. position adjacent to the halogen, as demonstrated by quenching with CO2 to give the corresponding benzoic acids. In contrast, a mixt. of LiN(CHMe2)2 and KOCMe3 selectively deprotonates the benzylic positions of 2- and 3-FC6H4Me to give after quenching with CO2 the corresponding phenylacetic acids. With 3-(F3C)C6H4Me, metal/hydrogen exchange again occurs at the Me group while the corresponding 2- and 4-isomers do not produce interceptable organometallic intermediates. [on SciFinder (R)