By reaction of N-[(4-chlorobutyl)carbonyl]cyclohexylamine (I) first with PCl5 and then with NH3 in benzene to give 1-cyclohexyl-5-(4-chlorobutyl)tetrazole (II), which is treated with 6-hydroxy-3,4-dihydrocarbostyril (III) and 1,5-diazabicyclo[5.4.0]undecene-5 (DBU) in ethanol. Alternatively, the condensation can be performed by means of either NaOH, KOH or KOH / K2CO3 in a great variety of solvents.
The condensation of p-anisidine (IV) with 3-chloropropionyl chloride (V) by means of TEA in hot toluene, hot 2-butanone or DMF gives the corresponding amide (VI), which is then cyclized by means of AlCl3 in N,N-dimethylacetamide at 150-60 C and treated with NaBH4 in water to yield the desired 6-hydroxy-1,2,3,4-tetrahydroquinolin-2-one intermediate (III).