[OH:1][CH2:2][CH2:3][C:4]1[N:5]=[CH:6][C:7]([C:10]([O:12][CH3:13])=[O:11])=[N:8][CH:9]=1.[O:14]1[CH:19]=[CH:18][CH2:17][CH2:16][CH2:15]1.C1(C)C=CC(S([O-])(=O)=O)=CC=1.[NH+]1C=CC=CC=1.O>ClCCl>[O:14]1[CH2:19][CH2:18][CH2:17][CH2:16][CH:15]1[O:1][CH2:2][CH2:3][C:4]1[N:5]=[CH:6][C:7]([C:10]([O:12][CH3:13])=[O:11])=[N:8][CH:9]=1
To a solution of methyl 5-(2-hydroxyethyl)pyrazine-2-carboxylate (1.07 g) in dichloromethane (20 mL) were added 3,4-dihydro-2H-pyrane (1.6 mL) and pyridinium p-toluenesulfonate (295 mg) at room temperature, followed by stirring at room temperature overnight. To the reaction mixture was added water, followed by extraction with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate. The crude product obtained by concentration was purified by silica gel column chromatography (hexane:ethyl acetate=2:1-1:2) to obtain methyl 5-[2-(tetrahydro-2H-pyran-2-yloxy)ethyl]pyrazine-2-carboxylate (1.25 g) as a pale yellow oily substance.
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