O=[C:2]([C:9]1[CH:14]=[CH:13][CH:12]=[CH:11][C:10]=1[CH3:15])[CH2:3][CH2:4][CH2:5][C:6]([OH:8])=[O:7].[OH-].[K+].[BH4-].[Na+].Cl>O.C(OCC)(=O)C>[CH3:15][C:10]1[CH:11]=[CH:12][CH:13]=[CH:14][C:9]=1[CH:2]1[O:7][C:6](=[O:8])[CH2:5][CH2:4][CH2:3]1To a stirred suspension of 5-oxo-5-(2-methylphenyl)pentanoic acid (10 g) in water (100 mL) is added potassium hydroxide pellets (6.35 g). The temperature of the mixture is maintained at 2-20° C. whilst sodium borohydride (1.47 g) is added over 15 minutes. The reaction mixture is left at room temperature for 18 hours when 1 N hydrochloric acid (100 mL) is cautiously added followed by water (50 mL) and ethyl acetate (100 mL). The organic phase is separated and the aqueous phase extracted twice with ethyl acetate (100 mL). The combined organic phases are washed with brine (100 mL), dried over magnesium sulphate and evaporated to give 6-(2-methylphenyl)-tetrahydropyran-2-one (5.27 g) as a yellow oil.
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