Patent ID: 7524960

Claim:
A process of preparing 6-(4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy)-3,4-dihydro-2(1H)-quinolinone (Cilostazol), the process comprising: reacting 6-hydroxy-3,4-dihydroquinolin-2(1H)-one with 5-(4-chlorobutyl)-1-cyclohexyl-1H-tetrazole in the presence of a hydrated inorganic base, to thereby obtain a reaction mixture containing Cilostazol; isolating the Cilostazol from the reaction mixture; slurrying the Cilostazol in an organic solvent; and crystallizing the Cilostazol in the presence of a base, to produce Cilostazol, which is substantially free of N-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butyl]-6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone, and has a purity of at least 99.9%.