The process consists in condensing (2-methyl-6,7,8,9-tetrahydro-4 H-pyrido-[1,2-a]pyrimidin-3-yl)-acetaldehyd with 6-fluoro-3-piperidinyl)-1,2-benzisoxazole to yield the intermediate enamine, 3-{2-[4-(6-fluoro-benzo[d]isoxazol-3-yl)-piperidin-1-yl]vinyl}-2- -methyl-6,7,8,9-tetrahydro-pyrido[1,2,-a]pyrimidin-4 -one followed by reduction of such an enamine.