Fluorophenols and (Trifluoromethyl)phenols as Substrates of Site-Selective Metalation Reactions: To Protect or not To Protect

O-Methoxymethyl (MOM) protected fluorophenols can be cleanly metalated and subsequently be submitted to site-selective electrophilic substitution. The 2- and 4-isomers exhibit ambivalent reactivity: deprotonation occurs at the position adjacent to the oxygen when butyllithium is employed whereas the position adjacent to the fluorine is attacked by the superbasic mixture of butyllithium and potassium tert-butoxide (LIC-KOR). The MOM-protected (trifluoromethyl)-phenols react exclusively at oxygen-neighboring positions. The meta isomer provides another example of optional site selectivity, undergoing hydrogen/metal exchange at the 2-position with the LIC-KOR reagent and at the 6-position with sec-butyllithium. Unprotected (trifluoromethyl)phenols can also be ortho-metalated after O-deprotonation, although the products are formed in only moderate yields.