The intermediate phenylenediamine (VI) was prepared as follows. Reaction of 5-chloro-2-nitroaniline (I) with sodium methoxide afforded 5-methoxy-2-nitroaniline (II), which was subsequently converted to the N-Boc derivative (III). Methylation of (III) with iodomethane and NaH, followed by acidic treatment of the resulting N-methyl carbamate (IV), produced the N-methyl aniline (V). The nitro group of (V) was then reduced with the combination SnCl2-NaBH4 to furnish the diamine (VI).
Alkylation of 5-(4-hydroxybenzyl)-3-tritylthiazolidine-2,4-dione (VII) with methyl bromoacetate (VIII) in the presence of cesium carbonate gave rise to the aryloxy acetate (IX). Subsequent cleavage of the N-trityl protecting group of (IX) was achieved by treatment with HOAc in aqueous dioxan at 80 C. The resulting ester (X) was finally condensed with phenylenediamine (VI) to produce the target benzimidazole.