| abstract |
The subject invention concerns a process for the preparation of a compound of formula (2), which comprises phenolic oxidation of a compound of formula (1) wherein X 1 and X 2 are independently selected from H or a protecting group for the phenolic function, e.g. acyl or trialkylsilyl; groups A 1 , A 2 , B 1 , B 2 and Y are selected so as to render the nitrogen atom non-basic; Z is a blocking group, e.g. Br or t-butyl; and R is H, C 1-20 alkyl, C 3-20 aryl, C 4-20 arylalkyl, and wherein the process is carried out in a two-phase liquid system comprising an aqueous base and an organic solvent having a dielectric constant below 4.8. |