合成路线1

3,4-Dichlorotoluene (I) was nitrated with HNO3 in H2SO4, and the resulting nitrotoluene (II) was condensed with diethyl oxalate in the presence of KOEt to give the phenylpyruvic derivative (III). Then, reductive cyclization of (III) with Fe and AcOH produced ethyl 5,6-dichloroindole-2-carboxylate (IV). Further reduction of (IV) with LiAlH4 yielded alcohol (V), which was oxidized to aldehyde (VI) with MnO2 in Et2O. Horner-Emmons reaction of (VI) with triethyl phosphonoacetate (VII) afforded the indolylpropenoate (VIII). This was reduced to the allyl alcohol (IX) with DIBAL-H, and subsequently oxidized with MnO2 to afford the propenaldehyde (X). In a shorter procedure, Wittig reaction of (VI) with formylmethylene triphenylphosphorane (XI) yielded also propenaldehyde (X) along with the homologated pentadienaldehyde. Phosphonium bromide (XIV) was prepared by bromination of methyl methoxyacetate (XII) with NBS in the presence of dibenzoyl peroxide, followed by condensation of the resulting bromide (XIII) with PPh3. Wittig reaction of this phosphonium reagent with aldehyde (X) in the presence of DBU in boiling THF gave ester (XV). Subsequent saponification of (XV) with ethanolic KOH yielded acid (XVI). The aminopiperidine (XX) was synthesized by N-methylation of tetramethylpiperidone (XVII), followed by formation of the oxime (XIX) and catalytic reduction over Rh/C. Then, condensation of amine (XX) with acid (XVI) using 1-ethyl-3-(dimethylaminopropyl)carbodiimide-HCl (EDC) and 1-hydroxy-7-azabenzotriazole (HOAt) in DMF furnished the target compound.