A solution of ethyl 4-(2,3-dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-4-methyl-3-oxo-pentanoate (2.0 g), lithium hydride(0.11 g) in 1,2-dimethoxyethane and hexamethylphosphoramide was stirred at 40° C. for 1 hour. cis-1,4-Dichloro-2-butene was then added, and the mixture stirred at 65° C. for 48 hours. The mixture was extracted with ether, washed with brine, dried (magnesium sulphate), evaporated and purified by column chromatography eluting with ethyl acetate/hexane (1:5) to give ethyl 1-[2-(2,3-dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-2-methylpropionyl]cyclopent-3-enylcarboxylate (Compound 9, 0.62 g), NMR: 1.20(3H, t), 1.52(6H, s), 1.91(3H, s), 3.0-3.25(4H, m), 4.14 (2H, q), 5.17(2H, s), 5.56(2H, s), 7.2-7.4(5H, m).
