4-Bromobenzotrifluoride (I) is converted to the corresponding Grignard reagent (II), which undergoes addition to diethyl oxalate, yielding keto ester (III). Subsequent saponification of ester (III) gives the phenylglyoxylic acid derivative (IV). Condensation of (IV) with 5-chloro-2-methoxyphenylhydrazine (V) affords the aryl hydrazone (VI). Curtius rearrangement of the carboxyl moiety of (VI) by means of diphenylphosphoryl azide generates the corresponding isocyanate, which spontaneously cyclizes to the triazolone (VII). Methyl ether cleavage in (VII) with boron tribromide gives rise to the title phenol derivative.
Acylation of 5-chloroanisidine (I) with 3,5-bis(trifluoromethyl)benzoyl chloride (II) affords benzamide (III). Treatment of amide (III) with PCl5, followed by reaction of the intermediate iminoyl chloride with hydrazine in THF generates the amidrazone (IV). Cyclization of (IV) with carbonyl diimidazole leads to triazolone (V). Finally, methyl ether cleavage in (V) employing pyridine hydrochloride at 225 C provides the target phenol compound.