1) The cyclization of 2,3-dimethylaniline (I) with diethyl acetylmalonate (II) in 1-chloronaphthalene at 240 C gives 3-acetyl-4-hydroxy-7,8-dimethylquinolin-2(1H)-one (III), which by reaction with diethyl oxalate (IV) by means of sodium ethoxide in refluxing benzene yields ethyl-4-(4-hydroxy-7,8-dimethyl-2-oxo-1,2-dihydroquinolin-3yl)-2,4-dioxo-butanoate (V). The cyclization of (V) in acetic acid concentrated HCl at 100 C affords 5,6-dihydro-7,8 dimethyl-4,5-dioxo-4H-pyrano[3,2-c]quinoline-2-carboxylic acid (VI), which is converted into the corresponding acyl chloride (VII) by reaction with refluxing SOCl2. Finally, this compound is treated with hot 3-methylbutanol (VIII).
2) The condensation of quinolone (III) with 3 methylbutyl oxalate (X) [obtained from 3 methyl butanol (VIII) and oxalic acid (IX)] by means of NaH yields 3-methylbutyl-4-(4 hydroxy-7,8-dimethyl-2-oxo-1,2-dihydroquinolin-3-yl)-2,4-dioxobutanoate (XI), which is then cyclized by means of sulfuric acid. ([*]-labeled compound).