Isopropyl magnesium bromide (0.7M solution in tetrahydrofuran) was added to a solution of monoethyl malonate(1.44 g) in tetrahydrofuran at 0° C. The mixture was stirred at 20° C. for 0.5 hour and at 40° C. for 0.5 hour. 2-(2,3-Dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)2-methylpropionic acid (2 g) and carbonyldiimidazole (1.42 g) was stirred in tetrahydrofuran for 8 hours and the resulting imidazolide solution then added to the above mixture at 0° C., stirred at 20° C. for 3 hours and refluxed for 2 hours. The mixture was diluted (ether), washed (5% hydrochloric acid), dried (MgSO4),evaporated and the residue purified by column chromatography (ethyl acetate/hexane 1:2) to give ethyl 4-(2,3-dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-4-methyl-3-oxo-pentanoate (Compound 200, 1.4 g), NMR 1.25(3H, t), 1.47(6H, s), 1.94(3H, s), 3.60(2H, s), 4.15(2H, q), 5.26(2H, s), 7.2-7.4(5H, m).
