Br[CH2:2][CH2:3][CH:4]=[CH2:5].[Mg].[CH3:7][C:8]1[O:13][CH2:12][N:11]([C:14]([CH3:18])([CH3:17])[CH:15]=[O:16])[C:10](=[O:19])[C:9]=1[C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1.[Cl-].[NH4+]>O1CCCC1.C(OCC)(=O)C>[CH3:7][C:8]1[O:13][CH2:12][N:11]([C:14]([CH3:17])([CH:15]([OH:16])[CH2:5][CH2:4][CH:3]=[CH2:2])[CH3:18])[C:10](=[O:19])[C:9]=1[C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1
4-Bromobut-1-ene (approximately 0.2 g) was added to a suspension of magnesium (0.17 g) in tetrahydrofuran, under an inert atmosphere at 20° C. Once the reaction had initiated, further 4-bromobut-1-ene (approximately 0.67 g) in tetrahydrofuran was added over 10 minutes. After refluxing for 1 hour, the mixture was cooled to -5° C. and a solution of 2-(2,3-dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-2-methylpropionaldehyde (1.00 g) in tetrahydrofuran was added over 20 minutes. After stirring for 18 hours, ammonium chloride and ethyl acetate were added and the organic phase washed (brine), dried (magnesium sulphate) and evaporated to give 2-(2,3-dihydro-6-methyl-4-oxo-5-phenyl-4H-1,3-oxazin-3-yl)-2-methylhept-6-en-3-ol (0.68 g) as a white solid, m.p. 74-75° C.
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