Acylation of 4-piperidone ethylene ketal (I) with 3-chloro-4-fluorobenzoyl chloride (II) in the presence of Et3N gave amide (III). After ketal hydrolysis of (III) using 80% formic acid and CuSO4, treatment of the resulting N-acyl piperidone (IV) with dimethyloxosulfonium methylide provided epoxide (V). Subsequent ring opening of (V) with HF-pyridine complex afforded the fluoro alcohol (VI), which was converted to tosylate (VII). Then, Gabriel synthesis via the corresponding phthalimide (VIII) produced amine (IX). The pyridine-2-carboxaldehyde (XII) was prepared by reduction of ethyl 6-chloro-5-methylpyridine-2-carboxylate (X) with NaBH4, followed by displacement of the chloro group by ethanolic methylamine in a sealed vessel at 100 C yielding pyridinealcohol (XI), which was further oxidized to the desired aldehyde (XII) using MnO2. The title compound was then obtained by condensation of amine (IX) with aldehyde (XII), followed by reduction of the intermediate imine with KBH4 in MeOH.

Ring opening of epoxide (I) with hydrogen fluoride-pyridine complex affords the fluorohydrin (II). After conversion of (II) to the corresponding tosylate (III), reaction with potassium phthalimide in boiling DMF furnishes the substituted phthalimide (IV). Hydrolysis of phthalimide (IV) in hot ethanolamine gives rise to the primary amine (V). Condensation of (V) with 5-methylpyridine-2-carbaldehyde (VI) leads to imine (VII). Finally, reduction of imine (VII) to the corresponding amine with methanolic KBH4, followed by conversion to the fumarate salt provides the title compound.

In an alternative, shorter route, 1-(3-chloro-4-fluorobenzoyl)-4-piperidinone (I) is subjected to Darzens condensation with chloroacetonitrile in the presence of NaOH and a phase-transfer catalyst to furnish the epoxy nitrile (II). Epoxide opening in (II) with HF-pyridine gives rise to the fluoro hydroxy nitrile (III). This is finally condensed with (5-methylpyridin-2-yl)methylamine (IV) under reductive amination conditions to produce the title compound.