A solution of 1-benzyl-3-ethoxycarbonyl-4-hydroxy-6-methyl-2(1H)-quinolinone obtained in Step (3) of Preparation A (12.4 g) in dichloromethane (50 ml) and methanol (10 ml) was treated with excess diazomethane in ether for 10 mins and was then evaporated. The crude methylation product, upon chromatography on silica gel, yielded 1-benzyl-3-ethoxycarbonyl-4-methoxy-6-methyl-2(1H)-quinolinone (11.5 g). This product (7.13 g) in dry toluene (80 ml) was cooled to -78° C. and a 1M solution of di-isobutyl aluminum hydride (30 ml) was added dropwise in 10 min. After 2.5 hours stirring at -78° C. the reaction mixture was worked up by stirring with aqueous ammonium chloride/1N hydrochloric acid followed by extraction with methylene chloride. The crude reduction product was chromatographed on silica gel and crystallized from ethyl acetate/hexane to give 1-benzyl-3-formyl-4-methoxy-6-methyl-2(1H)-quinolinone as a yellow solid (7.8 g). That the expected product was obtained was confirmed by the spectral data: NMR (CDCl3): δ2.40 (s, 3H, CH3), 4.18 (s, 3H, OCH3), 10.58 (s, 1H, CHO); MS (FAB): m/e 308 (M.+ +1).
