Br[C:2]1[CH2:6][CH2:5][CH2:4][CH:3]=1.[Mg].[Br-].[CH3:9][C:10]1[O:15][CH2:14][N:13]([C:16]([CH3:20])([CH3:19])[CH:17]=[O:18])[C:12](=[O:21])[C:11]=1[C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=1.Cl>O1CCCC1.BrCCBr.C(OCC)(=O)C>[CH3:9][C:10]1[O:15][CH2:14][N:13]([C:16]([CH3:19])([CH3:20])[CH:17]([C:2]2[CH2:6][CH2:5][CH2:4][CH:3]=2)[OH:18])[C:12](=[O:21])[C:11]=1[C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=1A part of a solution of 1-bromocyclopent-1-ene (3.9 g) in tetrahydrofuran was added to a stirred mixture of magnesium turnings (0.68 g) and 1 drop of 1,2-dibromoethane in tetrahydrofuran at 20° C. under an inert atmosphere. The mixture was heated to reflux and the remaining bromide solution added dropwise over 15 minutes. The mixture was stirred for 0.5 hour, cooled to 0° C., and a solution of 2-(2,3-dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-2-methylpropionaldehyde (4.0 g) in tetrahydrofuran added below 10° C. The mixture was stirred for 1 hour and ethyl acetate and hydrochloric acid (1N) added. The organic phase was washed (brine), dried (magnesium sulphate), evaporated and purified by silica gel column chromatography, eluting with n-hexane/ethyl acetate (2:1) to give 2-(2,3-dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-2-methyl-1-(cyclopent-1-enyl)propan-1-ol (4.95 g), NMR: 1.45(s,3H), 1.60(s,3H), 1.90(s,3H), 1.80-1.92(2H), 2.15-2.53(4H), 4.37(d,1H), 5.04(d,1H), 5.20-5.30(2H), 5.63(s,1H), 7.22-7.41(5H).
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