[O:1]1[CH:6]=[CH:5][CH2:4][CH2:3][CH2:2]1.[CH2:7]([OH:12])[CH:8]=[CH:9][CH2:10][OH:11].C1(C)C=CC(S([O-])(=O)=O)=CC=1.[NH+]1C=CC=CC=1>ClCCl.O1CCCC1>[O:1]1[CH2:2][CH2:3][CH2:4][CH2:5][CH:6]1[O:11][CH2:10]/[CH:9]=[CH:8]\[CH2:7][OH:12]Dihydropyran (9.1 ml, 100 mmol) was added dropwise to a cooled (0° C.) solution of 2-butene-1,4-diol (8.8 g, 10 mmol) and pyridinium paratoluenesulfonate (0.25 g, 10 mmol) in anhydrous dichloromethane:tetrahydrofuran (2:1). The mixture was stirred two days at 0° C. then concentrated in vacuo. The residue was purified by flash chromatography on silica gel (ethyl acetate:hexane 3:7) to give 8.3 g of the title compound (49%).
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