反应详情

Methyl-2-lithio propionate is generated from methyl propionate (176 mg, 2 mM) and lithium diisopropylamide (2 mM) in tetrahydrofuran (5 ml) under nitrogen in the usual manner. To this reagent, (1RS,4SR,5RS)-4-(3-methanesulfonyloxypropyl)-4-methyl-3,8-dioxabicyclo[3.2.1]octane-1-ethanol (258 mg, 0.84 mM) in tetrahydrofuran (5 ml) is slowly added at -78° C. and stirred for two hours. The resulting mixture is allowed to warm to room temperature and stirred for an additional hour. This mixture is then poured into saturated aqueous ammonium chloride solution (5 ml) and extracted with ether (5×10 ml). The combined organic layers are dried (Na2SO4), the solvent is removed in vacuo and the residue is purified by column chromatography on silica gel (30 g) with ether-petroleum ether (4:1) to give (1RS,4SR,5RS)-4-(4-carbomethoxypentyl)-4-methyl-3,8-dioxabicyclo[3.2.1]octane-1-ethanol (71 mg, 30%) as a colorless oil.

1. stirringstirred for an additional hour
2. extractionextracted with ether (5×10 ml)
3. dry with materialThe combined organic layers are dried (Na2SO4)
4. customthe solvent is removed in vacuo
5. customthe residue is purified by column chromatography on silica gel (30 g) with ether-petroleum ether (4:1)