[OH:1][C@H:2]([CH3:7])[CH2:3][C:4]([OH:6])=[O:5].[C:8]1([CH2:14][CH2:15][CH:16]=O)[CH:13]=[CH:12][CH:11]=[CH:10][CH:9]=1.C1(C)C=CC(S(O)(=O)=O)=CC=1.[NH+]1C=CC=CC=1.O>ClCCl>[C:8]1([CH2:14][CH2:15][C@H:16]2[O:5][C:4](=[O:6])[CH2:3][C@@H:2]([CH3:7])[O:1]2)[CH:13]=[CH:12][CH:11]=[CH:10][CH:9]=1A mixture of (R)-3-hydroxybutanoic acid (7.8 g), 3-phenylpropionaldehyde (6.71 g) and pyridinium toluene-4-sulphonic acid (ca. 10 mmol %) in dichloromethane (300 ml) was stirred, under reflux, for 48 hours with removal of water. The reaction mixture was cooled to room temperature, washed three times with saturated sodium bicarbonate, dried (MgSO4) and evaporated under reduced pressure. The residue was crystallised from ether/pentane to give (2R,6R)-2-(2'-phenylethyl)-6-methyl-1,3-dioxan-4-one (7.0 g), m.p. 49.7°-50.9° C.; [α]DR.T. =15.2(c=1.05; CHCl3).
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