[CH2:1]([O:3][C:4]([CH:6]1[CH2:11][CH2:10][O:9][CH2:8][C:7]1=O)=[O:5])[CH3:2].[CH3:13][C@@H:14]([NH2:21])[C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1>C1C=CC=CC=1.O.C1(C)C=CC(S(O)(=O)=O)=CC=1>[CH2:1]([O:3][C:4]([C:6]1[CH2:11][CH2:10][O:9][CH2:8][C:7]=1[NH:21][C@@H:14]([C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1)[CH3:13])=[O:5])[CH3:2]A solution of 3-oxo-tetrahydro-pyran-4-carboxylic acid ethyl ester (3.03 g, 17.6 mmol), R-(+)-α-methylbenzylamine (2.35 g, 19.4 mmol) and p-toluenesulfonic acid hydrate (67 mg, 230 μmol) in benzene (60 mL) was heated at reflux under a Dean-Stark trap for 16 h. The cooled mixture was concentrated in vacuo to provide the product as a yellow oily semisolid (5.05 g), used without further purification.
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