Three chloro(trifluoromethyl)pyridines as model substrates for regioexhaustive functionalization

As a further test of the concept of regioexhaustive functionalization, 2-chloro-6-(trifluoromethyl)pyridine, 2-chloro-5-(trifluoromethyl)pyridine and 3-chloro-4-(trifluoromethyl)pyridine were each converted into the three possible carboxylic acids. This was achieved by employing several, but not all of the organometallic "toolbox methods"; transformation of a more basic organometallic species into a less basic isomer by transmetalation-equilibration, site discriminating deprotonation with lithium N,N-diisopropylamide or lithium 2,2,6,6-tetramethylpiperidide, regio-divergent iodine migration and steric screening of acidic positions by a bulky trialkylsilyl group. [on SciFinder (R)]