The condensation between 5-chloro-2-nitrobenzoyl chloride (I) and 2-amino-5-chloropyridine (II) produced the corresponding amide (III). Subsequent catalytic hydrogenation of the nitro group of (III) gave aniline (IV). Acid chloride (VI), prepared from N-Boc-isonipecotic acid (V) and oxalyl chloride, was then coupled to aniline (IV) to furnish amide (VII). Further trifluoroacetic acid-promoted cleavage of the Boc protecting group of (VII) yielded piperidine (VIII). Finally, reductive alkylation with acetone in the presence of sodium triacetoxyborohydride gave rise to the target N-isopropyl piperidine.
An alternative preparation for the title compound consisted in the reductive alkylation of ethyl isonipecotate (IX) with acetone to afford the N-isopropyl isonipecotate (X). After basic hydrolysis of the ethyl ester group of (X), the resulting carboxylic acid (XI) was activated as the mixed anhydride (XII) with isobutyl chloroformate. Anhydride (XII) was finally coupled to aniline (IV) to generate the required amide.