由醇合成醛酮
活性二氧化錳
活性 MnO2 廣泛用于氧化α,β-不飽和基團(tuán)（三鍵，雙鍵、芳香環(huán)）的醇，可選擇性氧化烯丙式醇，條件溫和，不會(huì)引起雙鍵的異構(gòu)化MnO2 的活性及溶劑的選擇對(duì)反應(yīng)至關(guān)重要，常用的溶劑有二氯甲烷、乙醚、石油醚、己烷、丙酮等。
1 用活性MnO2 氧化示例一:
A 500-mL, round-bottomed flask, equipped with a Teflon-coated magnetic stirring bar, is charged with the 11.2 g of allylic alcohol and 300 mL of dichloromethane, and the resulting vigorously stirred solution is treated with 33 g of active manganese dioxide (380 mmol). Additional 2–5 g lots of the oxidant are added every 2–3 hr until the reaction is complete. The reaction mixture is vacuum-filtered through a pad of diatomaceous earth, and the pad is washed with 200 mL of dichloromethane. The resulting clear filtrate is concentrated carefully using a rotary evaporator, and the residual oil is purified by bulb-to-bulb distillation at 0.3 mm (pot temperature 100 °C) affording 8.43–8.71 g (87–90%) of enone as a pale yellow oil that solidifies when cooled below 15°C. Crystallization of the crude product from pentane at ?70 °C gives (4S)-(?)-tert-butyldimethylsiloxy-2-cyclopenten-1-one as colorless needles having mp 32–33 °C, [α]D23 ?65.1° (CH3OH, c 0.94).
Reference: Organic Syntheses, Coll. Vol. 9, p.136; Vol. 73, p.44
2 用活性MnO2 氧化示例二:
