To a stirred mixture of 4 parts of a sodium hydride dispersion 60% in 180 parts of methylbenzene are added dropwise 12 parts of ethyl 3-oxobutanoate at room temperature. Then there is added 1 part of N,N,N-tridecylmethanammonium chloride and the whole is warmed to 40° C. At this temperature, a solution of 25 parts of [1-(3-chloropropyl)-4-piperidinyl](4-fluorophenyl)methanone in 45 parts of methylbenzene is added slowly. The whole is heated to reflux and stirring is continued overnight at reflux temperature. The reaction mixture is cooled to room temperature and filtered over Hyflo. The filtrate is evaporated, yielding 24 parts of ethyl α-acetyl-4-(4-fluorobenzoyl)-1-piperidinepentanoate as a residue.
