Catalytic hydrogenation of tetrahydropyridine (I) produced piperidine (II). Alkylation of (II) with N-(3-bromopropyl)phthalimide (III) gave (IV). Subsequent hydrazinolysis of the phthalimido group of (IV) yielded amine (V). In a related procedure, piperidine (II) was alkylated with N-Boc-3-bromopropylamine (VI) to give (VII), which was deprotected with HCl in EtOAc to give the diamino precursor (V).
The cyclization between 3,4-difluorobenzaldehyde (VIII), methyl 4-methoxyacetoacetate (IX) and urea (X) in the presence of cuprous oxide and boron trifluoride etherate gave rise to racemic pyrimidinone (XI). Optical resolution of (XI) by means of chiral HPLC furnished the desired (-)-enantiomer (XII), which was then hydrolyzed to carboxylic acid (XIII). Alternatively, kinetic resolution of (XI) by enzymatic hydrolysis using subtilistin furnished the desired (-)-carboxylic acid (XIII), which was then separated from the unreacted (+)-ester. Finally, coupling of carboxylic acid (XIII) with amine (V) using EDC and HOBt yielded the title amide.