OCC([NH:6][C:7](=[O:16])[CH2:8][CH2:9][C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1)CO.OC1C=CC(C=O)=CC=1.C1(C)C=CC(S(O)(=O)=O)=CC=1>C1(C)C=CC=CC=1>[C:10]1([CH2:9][CH2:8][C:7]([NH2:6])=[O:16])[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1A mixture of N-(2-hydroxy-1-hydroxymethyl-ethyl)-3-phenyl-propionamide (1.7 g, 7.6 mmol), toluene (70 ml), 4-hydroxybenzaldehyde (1.856 g, 15.2 mmol) and a catalytic amount of p-toluenesulfonic acid was refluxed for 3 h. The mixture was evaporated and CH2Cl2 was added to the residue. The precipitate was filtered off and recrystallised from hot AcOEt (50 ml). The light brown crystals formed collected yielding trans-N-12-(4-hydroxy-phenyl)-[1,3]dioxan-5-yl]-3-phenyl-propionamide (1.41 g, MS: m/e=328.2 (M+H+)). The filtrate was concentrated and left at 4° overnight. The newly formed crystals are collected yielding cis-N-[2-(4-hydroxy-phenyl)-[1,3]dioxan-5-yl]-3-phenyl-propionamide (0.401 g, m/e=326.4 (M−H+)).
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