烯烃及芳环的 C=C 双键经臭氧、氧化锇等作用而氧化断裂生成醛，是醛的重要合成法之一。此外，将烯烃变为醛的方法尚有用在 Rh 及 Co 催化下与氢及一氧化碳起反应的加氢甲酰化，硼氢化反应以及将芳环上的 C-H 直接转化为 Li 而起甲酰化反应等。
烯烃经加成-氧化、加成-还原、加成-水解、加成异构化以及一氧化碳插入反应等则能合成酮。
由烯烃臭氧氧化合成醛 烯烃及芳香环等与臭氧反应，先生成过氧化物，由于有爆炸危险不予分离，直接将其还原为醛。还原可用催化氢化、锌、碘化钠、磷化氢类化合物、亚磷酸、甲硫醚等方法。要是不予还原则经氧化分解得酸。 有多个双键共存时，臭氧化的选择性一般在电子密度高而位阻小的双键。芳香环的反应较迟钝，有不饱和侧链存在时优先选择氧化侧链双键。含杂原子的芳环对臭氧的稳定性大于苯环。 由烯烃臭氧氧化合成醛示例 1 ：
A dry, 100-mL, round-bottomed flask containing a magnetic stirring bar is fitted with an inlet adapter for ozonolysis and charged with 1-cyclopenteneacetonitrile (5.0 g, 46.7 mmol, and 60 mL of dry dichloromethane. A gentle stream of dry ozone is passed through the solution and the flask is immediately cooled to −78°C. Ozonolysis is continued until the distinctive blue color of excess ozone is first observed, ozonolysis is then terminated, and the excess ozone is removed by purging with a stream of nitrogen for 5-10 min. The solution is allowed to warm to room temperature, the ozonolysis adapter is replaced with a rubber septum, and neat dimethyl sulfide (3.9 g, 62.1 mmol) is added via syringe. The solution is allowed to stir at room temperature for 36 hr during which time the solution changes in color from a pale yellow to dark red. The resulting solution is concentrated under reduced pressure using a rotary evaporator, and the resulting thick, red syrup is diluted with 40 mL of ethyl acetate and washed with water (3 × 25 mL. The aqueous phase is extracted with ethyl acetate (3 × 25 mL), the organic phases are combined, rinsed with brine in order to remove all DMSO, dried (MgSO 4 ), filtered, and concentrated. The residual red oil (5.55 g, 98%) contains only trace impurities and can be used without purification in most cases. If required, further purification is achieved by rapid radial chromatography on a 2-mm plate using the solvent delivery tip designed for a 4-mm plate and eluting with 50% ethyl acetate-hexane. The desired fractions are combined and concentrated to provide 1-oxo-2-cyclohexenyl-2-carbonitrile (4.8g, 85% yield) as a pink oil.
由烯烃臭氧氧化合成醛示例 2：
A 500 mL, three-necked, round-bottomed flask is fitted with a glass tube to admit ozone, a calcium chloride drying tube, a glass stopper, and a magnetic stirring bar and is charged with 6.161 g of cyclohexene (0.075 mol), 250 mL of dichloromethane, and 50 mL of methanol. The flask is cooled to ca. −78°C (2-propanol–dry ice), and ozone is bubbled through the solution with stirring. When the solution turns blue, ozone addition is stopped. Nitrogen is passed through the solution until the blue color is discharged and then the cold bath is removed. The drying tube and ozone inlet are replaced with a stopper and rubber septum, and 1.215 g of p-toluenesulfonic acid (TsOH) (10% w/w) is added. The solution is allowed to warm to room temperature as it stirs under an atmosphere of nitrogen for 90 min. Anhydrous sodium bicarbonate (2.147 g, 4 mol-equiv) is added to the flask and the mixture is stirred for 15 min, and then 12 mL of dimethyl sulfide (0.150 mol) is added. After being stirred for 12 hr, the heterogeneous mixture is concentrated to approximately 50 mL by rotary evaporation. Dichloromethane (100 mL) is added and the mixture is washed with 75 mL of water. The aqueous layer is extracted with two more 100-mL portions of dichloromethane,and the combined organic layers are washed with 100 mL of water. After extracting the aqueous layer with 100 mL of dichloromethane, the organic layers are dried over anhydrous magnesium sulfate, filtered, and concentrated by rotary evaporation. Short-path distillation of the crude product gives 8.2–8.4 g of 6,6-dimethoxyhexanal, 68–70%, bp 80–82°C/1.75 mm.
