By reaction of 4-nitro-4?aminodiphenylamine (I) with N,N-diethylthiocarbamoyl chloride (II), ammonium thiocyanate (III), thiophosgene (IV), or bis-(N,N-diethylthiocarbamoyl)disulfide (V) in the appropriate solvent
Methylation of 2,6-diisopropylphenol (I) with iodomethane and K2CO3 provides ether (II). Subsequent treatment with iodine and nitric acid gives rise to the diaryl iodonium compound (III), isolated as the corresponding tetrafluoroborate salt. 3,5-Dibromo-4-hydroxybenzoic acid (IV) is esterified with methanol and thionyl chloride to produce (V). Copper-promoted coupling between hydroxybenzoate (V) and the diaryl iodonium salt (III) leads to diaryl ether (VI). Finally, simultaneous cleavage of the methyl ether and ester groups of (VI) is achieved by means of boron tribromide in cold CH2Cl2