3-[(Z)-6-methoxycarbonyl-2-hexenyl]-4-methoxymethylenetetrahydropyran → 4-formyl-3-[(Z)-6-methoxycarbonyl-2-hexenyl]tetrahydropyran

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A solution of 3-[(Z)-6-methoxycarbonyl-2-hexenyl]-4-methoxymethylenetetrahydropyran in a mixture of methanol (10 ml) and 50% aqueous trifluoroacetic acid (10 ml) was stirred at room temperature for 1 hour and the solvent was evaporated in vacuo to give 4-formyl-3-[(Z)-6-methoxycarbonyl-2-hexenyl]tetrahydropyran as a residue. The residue was dissolved in methanol (10 ml). To the solution were added 4-phenylsemicarbazide (200 mg) and sodium cyanoborohydride (100 ml) and the mixture was stirred at room temperature for 2 hours. The mixture was diluted with chloroform (50 ml) and the solution was washed successively with saturated aqueous sodium hydrogen carbonate and brine. The solution was dried over magnesium sulfate and the solvent was evaporated in vacuo. The residue was chromatographed on a silica gel column (10 g) with a mixture of n-hexane and ethyl acetate (3:1) as an eluent to give 3-[(Z)-6-methoxycarbonyl-2-hexenyl]-4-(4-phenylsemicarbazidomethyl)tetrahydropyran (266 mg) as a pale yellow oil.

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