A mixture of 3-(2-chloroethyl)-9-hydroxy-2-methyl-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidin-4-one (formula-8) (170.1 grams), 6-fluoro-3-(4-piperidinyl)-1,2-benzoisoxazole monohydrochloride (formula-6) (150 grams), sodium carbonate (113.3 grams), and potassium iodide (9.7 grams) in acetonitrile (1.5 L) was heated to 85° C. The reaction mixture was heated at 85° C. for 6 hrs. The reaction mixture was then cooled to −10° C. and stirred for 1.5 hrs. The solid obtained was filtered, washed with cold acetonitrile. The wet solid was taken in water, and acetic acid was added to the mixture to adjust the pH to 4.0. The reaction mixture was treated with acidic carbon and filtered through hyflow bed. The filtrate was treated with sodium hydrosulphite (hydrose). The pH of the reaction mixture was adjusted to 12 by adding aqueous sodium hydroxide solution and stirred for 45 min. The solid obtained was filtered, washed with water and dried to provide the title compound.
