A mixture of ethyl 4-(2,3-dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-4-methyl-3-oxo-pentanoate (0.5 g), 1,4-diiodobutane(0.23 ml) and potassium carbonate(1.0 g) was stirred in dimethylsulphoxide at 20° C. for 12 hours. The mixture was diluted (ether), washed (brine), dried (MgSO4), evaporated and the residue purified by column chromatography (ethyl acetate/hexane 1:3) to give ethyl 4-(2,3-dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-2-(4'-iodobutyl)-4-methyl-3-oxo-pentanoate (0.3 g), NMR 1.24(3H, t), 1.3-1.4(2H, m), 1.43((3H, s), 1.48(3H, s), 1.7-2.0(7H, m), 3.12(2H, t), 3.8-3.9(1H, m), 4.1-4.2(2H, m), 5.28(2H, d), 7.2-7.4(5H, m).
