General procedure for the synthesis of 2-hydroxy-4-(trifluoromethyl)benzoic acid from 4-trifluoromethylbenzoic acid:
III. Pd(II)-catalyzed tert-butyl hydroxylation reaction (General Method 02):
Pd(OAc)2 (11.2 mg, 0.05 mmol), 4-trifluoromethylbenzoic acid (0.5 mmol), benzoquinone (54.0 mg, 0.5 mmol), KOAc (98.0 mg, 1 mmol), and N,N-dimethylacetamide (1.5 mL) were added to a 50 mL high-pressure reactor, and the unit was equipped with a magnetic stir bar.
After filling the reactor with O2 (20 atm), it was evacuated and filled again with O2 (5 atm, repeated twice).
The reaction mixture was stirred at 115 °C for 15 h and subsequently cooled to room temperature.
Post-reaction treatment and purification of the crude product was carried out as described previously for hydroxylation under 1 atm O2 conditions.
