Reductive alkylation of ethyl 4-oxopiperidine-3-carboxylate (I) with cyclooctane carboxaldehyde (II) in the presence of sodium triacetoxy borohydride provided the cyclooctylmethyl piperidine (III). Treatment of (III) with ammonium acetate gave the unstable enamine (IV), which was reduced to amine (V) with NaBH3CN and subsequently coupled with 2-fluoronitrobenzene (VI) in refluxing MeOH to furnish nitroaniline (VIIa-b) as a mixture of trans- and cis-isomers. After separation by silica gel column chromatography, the desired trans-isomer was hydrogenated in the presence of Pd/C to afford phenylenediamine (VIII). Cyclization of (VIII) with carbonyldiimidazole produced benzimidazolone (IX), which was N-alkylated with ethyl iodide and NaH to give (X). Reduction of the ester group of (X) with LiAlH4 yielded the corresponding alcohol as a racemate. Optical resolution was achieved using a Chiralpak AD column.
The chloroformylation of cyclooctanone (XI) with DMF and POCl3 gives 2-chloro-1-cyclooctenecarbaldehyde (XII), which is dechlorinated and hydrogenated with H2 over Pd/C to afford the desired intermediate (II).