合成路线1

Jones oxidation of 2-fluoro-4-methyl-1-nitrobenzene (XVIII) with CrO3 and H2SO4, followed by acetylation with Ac2O in AcOH yields the gemdiacetate (XIX), which by deacetylation with HCl in AcOH at 115 °C provides 3-fluoro-4-nitrobenzaldehyde (XX). Horner-Wadsworth-Emmons reaction of aldehyde (XX) with ethyl (diethoxyphosphoryl)acetate (XXI) using NaH in THF affords the unsaturated ester (XXII), which by fluoride substitution with methylamine (XXIII) in DMSO provides the nitro-aniline derivative (XXIVa) . Alternatively, condensation of 2,4-dichloro-1-nitrobenzene (XXV) with methylamine (XXIII) using Et3N in DMSO or THF yields 5-chloro-N-methyl-2-nitroaniline (XXVI), which is then subjected to Heck coupling with ethyl acrylate (XXVIIa), methyl acrylate (XXVIIb) or butyl acrylate (XXVIIa) in the presence of Pd(OAc)2, LiCl and DIEA in DMAc at 110 °C , or Pd2dba3, t-Bu3P and (c-Hex)2NMe at 110 °C to give the corresponding arylacrylates (XXIVa), (XXIVb) or (XXIVc). Reduction of the nitro group in compounds (XXIVa), (XXIVb) or (XXIVc) by means of SnCl2.2H2O in EtOH at 80 °C , H2 over Raney-Ni in toluene/MeOH or Na2S2O4 and K2CO3 in EtOH/H2O produces the corresponding diaminophenylacrylates (XXVIIIa) , (XXVIIIb) or (XXVIIIc) , which are finally condensed with 1-aminocyclo-butanecarboxylic acid hydrochloride (XXIX) in CH2Cl2 to provide the benzimidazole intermediates (IIIa) , (IIIb) or (XXX), the free base of intermediate (II) .
Similarly, intermediate (II) can be obtained by condensation of the diaminophenylacrylate (XXVIIIc) with N-Boc-1-aminocyclobutanecarboxylic acid (XXXI) using DCC in toluene, followed by N-deprotection and cyclization of the resulting amino amide (XXXII) with HCl in BuOH at 75 °C .