烯烴用 OsO4/NaIO4 合成醛氧化
與臭氧化法相比，OsO 4 /NaIO 4 是一種溫和的烯烴氧化開裂法，在天然產(chǎn)物合成中很有用。烯烴先與 OsO 4 反應生成鋨酸酯，再用過碘酸鈉氧化，發(fā)生開裂，在生成羰基化合物的同時，OsO 4 再生，所以 OsO 4 用催化量即可。當生成的醛易于分子內(nèi)縮合時，反應最好在兩相系統(tǒng)中進行。 烯烴用 OsO 4 /NaIO 4 氧化合成醛反應示例：
N-Benzyl-3-(Z/E)-ethylideneazetidin-2-one (5.0 g, 26.7 mmol) is dissolved in 150 mL of methanol and 100 mL of water contained in a 500-mL, one-necked, round-bottomed flask. Sodium metaperiodate (14.3 g, 67.0 mmol) is introduced, followed by approximately 40 mg of osmium tetraoxide. The reaction mixture is stirred vigorously for 12 hr under nitrogen, treated with Celite (6 g), and agitated for an additional hour prior to filtration. The filtrate is concentrated to 1/3 of its volume under reduced pressure, then extracted with ethyl acetate (2× 200 mL). The combined organic phases are washed once with brine, dried, and concentrated to leave a dark brown oil. This oil is flushed through a short pad of silica gel (8 cm × 8 cm) using dichloromethane as eluant (900 mL). The pure fractions are pooled and evaporated to give a clear pale yellow oil, which crystallizes on prolonged standing at 5°C. The yield of N-benzylazetidine-2,3-dione is 3.12-3.64 g (66.7-77.9%).
烯烴經(jīng)由有機硼化合物中間體的烯烴甲酰化合成醛 烯烴與甲硼烷反應所得的有機硼化合物能用各種方法轉(zhuǎn)變?yōu)槿?。用鉻酸氧化時，所得醛的碳原子數(shù)不變。如與一氧化碳反應再進行氧化便得多一個碳原子的醛。要是與重氮乙醛反應，即可得增長二個碳原子的醛。通過與丙烯醛的加成，碳原子數(shù)可增加三個。 由烯烴的加氫甲?；铣扇驶铣煞ǎ?/p> 將烯烴與水煤氣（CO 和水的混合物）在鈷、銠等催化劑存在下進行反應反應可得延長一個碳的醛。工業(yè)上需要高溫高壓下進行。將催化劑改良可使反應在常溫常壓下進行，已經(jīng)有了實驗室很有用的醛的合成法 由烯烴的加氫甲?；铣扇驶铣煞ǎ┓磻纠?/p>
To a stainless-steel, 0.5-l. pressure vessel equipped with a 450-atm. manometer and a temperature recorder is added 0.2 g. (0.8 mmole) of rhodium(III) oxide. The vessel is sealed and evacuated to 0.1 mm. pressure. A solution of 82 g. (1.0 mole) of cyclohexene in 140 ml. of anhydrous benzene is introduced by suction into the vessel. The vessel is placed in a heatable shaking device and pressured to 75 atm. with carbon monoxide; the total pressure is then increased to 150 atm. with hydrogen. Shaking is begun and the vessel is heated to an internal temperature of 100°. When the internal temperature reaches 100°, the pressure begins to fall. Whenever the pressure falls to 60 atm., rocking is stopped and the pressure is first increased to 105 atm. with carbon monoxide, then to 150 atm. with hydrogen. Rocking is started again, and the process is continued until no appreciable pressure decrease occurs. Approximately 2 hours is required, and the pressure decrease corresponds to the consumption of 2 moles of gas. The vessel is rapidly cooled to room temperature and the residual gas is carefully vented.
The vessel is opened, and the slightly yellow reaction mixture is transferred immediately to a 2-l., round-bottomed flask containing a freshly prepared solution of 200 g. of sodium hydrogen sulfite in 400 ml. of water. The flask is fitted with a stopper and is occasionally shaken at room temperature for a period of 3 hours. The resulting precipitate is collected by suction filtration on a sintered-glass funnel and washed with 500 ml. of diethyl ether. After drying in air, the bisulfite derivative is transferred to a 2-l. distillation flask containing 1 l. of 20% aqueous potassium carbonate. The resulting mixture is distilled, and the azeotropic mixture of water and aldehyde (b.p. 94–95°) is collected under nitrogen.
The aldehyde is separated from the lower aqueous layer as a colorless liquid, dried over 10 g. of anhydrous sodium sulfate, filtered, and distilled under reduced pressure using a Claisen distillation apparatus, yielding 92–94 g. (82–84%) of cyclohexanecarboxaldehyde, b.p. 52–53° (18 mm.), n D 25 1.4484. A purity of about 98% was established by GC analysis; the product is suitable for synthetic use without further purification.
