[Cl:1][C:2]1[CH:9]=[CH:8][C:5]([CH2:6][OH:7])=[C:4]([N+:10]([O-:12])=[O:11])[CH:3]=1.[O:13]1[CH:18]=[CH:17][CH2:16][CH2:15][CH2:14]1.[NH+]1C=CC=CC=1>ClCCl.C1(C)C(S([O-])(=O)=O)=CC=CC=1>[Cl:1][C:2]1[CH:9]=[CH:8][C:5]([CH2:6][O:7][CH:14]2[CH2:15][CH2:16][CH2:17][CH2:18][O:13]2)=[C:4]([N+:10]([O-:12])=[O:11])[CH:3]=1A magnetically stirred solution of 4-chloro-2-nitrobenzyl alcohol (25.0 g, 133 mmol) and 3,4-dihydro-2H-pyran (118.2 mL, 16.8 g, 200 mol) in anhydrous dichloromethane (250 mL) was treated at 25° C. with pyridinium (toluenesulfonate (PPTS, 50 mg). The solution was stirred for 12 h, washed with 1 N NaOH (250 mL), brine (250 mL), dried (K2CO3), filtered, and concentrated in vacuo. Silica gel chromatography (4:1 hexane:ethyl acetate) of the concentrate gave 22.5 g (62%) of the title compound as an oil.
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