Table 1. Optimization of trifluoromethylation of Ac-Tyr-NHMe with stoichiometric oxidant.

Entry	Solvent	pH	Yield (2 : 3) a
1	DMSO : H2O (2.5 : 1)	8.9	23 (22 : 1)
2	DMSO : 10% AcOH (aq) (2.5 : 1)	4.4	40 (31 : 9)
3	10% AcOH (aq)	2.2	63 (41 : 22)
4	20 mM Na citrate (aq)	4.0	66 (56 : 10)
5	160 mM NaOAc	5.5	57 (55 : 2)
6	MES buffer	6.0	8 (8 : <1)
7	Tris buffer	7.5	32 (32 : <1)
8	30 mM NaOH/borax	10	53 (48 : 5)

^aYield was determined by ¹⁹F-NMR spectroscopy using α,α,α-trifluorotoluene as an internal standard. Each entry is an average of at least two data points. MES = 2-(N-morpholino)ethanesulfonic acid.