A solution of dicyclohexylcarbodiinide (10.04 g) in N,N-dimethyeformaeide was added to a stirred solution of 2-(2,3-dihydro-6-methylthiomethyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-2-methylpropanoic acid (13.00 g) in N,N-dimethylformamide at 20° C. 2,5-Difluoroaniline (7.84 g) was added to the solution at 20° C. and the solution was stirred at ambient temperature for 18 hours. The reaction mixture was diluted with ethyl acetate then added to water and the fine suspension removed by filtration. The organic layer was washed in turn with 0.5M hydrochloric acid, brine, 1.0M sodium carbonate and brine and then dried (magnesium sulphate). The organic solution was evaporated under reduced pressure and the residue was purified by chromatography on silica gel, eluting with dichioromethane to give N-(2,5-difluorophenyl)-2-(2,3-dihydro-6-methylthiomethyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-2-methylpropanamide (Compound 3, 1.35 g) as a yellow solid, NMR (CDCl3) 1.68(s,6H), 2.10(s,3H), 3.22(s,2H), 5.30(s,2H), 6.64-6.76(m,1H), 6.95-7.05(m,1H), 7.25-7.38(m,5H), 8.11-8.21(m,2H).
