[F:1][C:2]([F:18])([F:17])[C:3]1[CH:4]=[C:5]([CH:8]=[C:9]([C:13]([F:16])([F:15])[F:14])[C:10]=1OC)[CH:6]=[O:7].B(Br)(Br)Br.[OH2:23]>ClCCl>[OH:23][C:4]1[C:3]([C:2]([F:18])([F:17])[F:1])=[CH:10][C:9]([C:13]([F:16])([F:15])[F:14])=[CH:8][C:5]=1[CH:6]=[O:7]3,5-Bis(trifluoromethyl)anisaldehyde (prepared as in Sui and Macielag, Synth. Commun. 1997, 27, 3581-3590, which is expressly incorporated by reference herein; 2.0 grams (g), 7.7 millimoles (mmol)) was dissolved in dry dichloromethane (CH2Cl2; 15 milliliters (mL)), cooled to −78° C. and treated in portions with boron tribromide (BBr3, 1 M solution in CH2Cl2; 8.0 mL, 8.0 mmol). The mixture was stirred and allowed to warm to 25° C. After 20 hours (h), the mixture was cooled to −40° C., carefully treated with H2O (10 mL) and warmed to room temperature. The separated organic phase was washed with water (H2O; 10 mL), saturated (satd) sodium chloride (NaCl) solution (5 mL), dried over sodium sulfate (Na2SO4) and evaporated. The residue was purified by silica gel chromatography with a 0 to 20% gradient of ethyl acetate (EtOAc) in hexane to give the purified aldehyde (1.4 g, 70%) as an oil: 1H NMR (400 MHz, CDCl3) δ 12.05 (s, 1H), 10.02 (s, 1H), 8.07 (s, 2H). EIMS m/z 258.
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