甲基可被许多氧化剂如 SeO2、铬酸、次卤酸等氧化为醛，特别是与羰基及芳香环 相邻的活性甲基更易氧化。其中 SeO2 的选择性较好，是常用的氧化方法之一。相比 之下，由亚甲基氧化合成酮的方法较多。主要有用 SeO2 氧化、用空气氧化、用铬酸氧 化、用高锰酸盐氧化、用醌氧化等方法。

 A 125-mL, three-necked, round-bottomed flask, equipped for mechanical stirring and outfitted with a reflux condenser, is charged with 20.0 g (0.13 mol) of (+)-camphor (1), 8.0 g (0.07 mol) of selenium dioxide, and 14.0 mL of reagent grade acetic anhydride. The green mixture is stirred at reflux for 1 hr, cooled to ambient temperature, and an additional 8.0 g (0.07 mol) of selenium dioxide is added. The mixture is again heated to reflux, and two further batches of 8.0 g (0.07 mol) of selenium dioxide are added at 2.5-hr and 6-hr intervals. After the reaction is heated at reflux for an additional 8 hr, during which time precipitation of selenium metal is observed, it is cooled to ambient temperature and transferred to a 125-mL beaker with the aid of 50 mL of ethyl acetate . The black precipitate is removed by filtration, and the filtrate is diluted with 100 mL of toluene. Concentration of the filtrate by rotary evaporation gives crude 2 as an orange solid. This is dissolved in 200 mL of ethyl acetate , and the solution is filtered by vacuum filtration through Celite. The filtrate is transferred to a 1-L separatory funnel and is washed successively with 200 mL of 10% aqueous sodium hydroxide solution and 100 mL of saturated aqueous sodium chloride solution. The organic solution is dried over magnesium sulfate , filtered, and concentrated by rotary evaporation to afford 20.89 g of crude (1R,4S)-(−)-camphorquinone (2) as yellow crystals, mp 198-199°C

    A 5-L, three-necked, Morton flask, equipped with a reflux condenser, thermometer, nitrogen inlet, and mechanical stirrer is charged with 81 g (0.59 mol) of potassium dihydrogen phosphate, 200 mL of water, and 2 L of p-dioxane. With vigorous mechanical stirring, 258 g (2.80 mol) of cycloheptatriene  is added, followed by 318 g (2.87 mol) of selenium dioxide. The mixture is heated to 90°C and maintained with vigorous stirring for 20 hr. After the black suspension is cooled to room temperature, 1 L of water is added and the mixture is filtered over Celite. The solution is divided into two halves and each is extracted with dichloromethane (2 × 1.5 L). Each organic extract is washed with saturated sodium bicarbonate solution (500 mL) and the solvent is removed under reduced pressure. The combined, crude, black oil is subjected to bulb-to-bulb distillation (20–110°C at 0.05 mm) with dry ice cooling. The resulting light brown liquid is fractionally redistilled (62–65°C at 0.25 mm) to give 147 g (50%) of tropone as a pale yellow oil. 

  In a 1-l. three-necked, round-bottomed flask, fitted with a liquid-sealed stirrer and a reflux condenser, are placed 600 cc. of dioxane, 111 g. (1 mole) of selenium dioxide, and 20 cc. of water. The mixture is heated to 50–55° and stirred until the solid has gone into solution, 120 g. (1 mole) of acetophenone is added in one lot, and the resulting mixture is refluxed with continued stirring for four hours. The hot solution is decanted from the precipitated selenium, and the dioxane and water are removed by distillation through a short column. The phenylglyoxal is distilled at diminished pressure from a 250-cc. Claisen flask, and the fraction boiling at 95–97°/25 mm. collected. The yield is 93–96 g. (69–72 per cent of the theoretical amount). 

    The aldehyde sets to a stiff gel on standing, probably as the result of polymerization. It may be recovered without appreciable loss by distillation. Phenylglyoxal may be preserved also in the form of the hydrate, which is conveniently prepared by dissolving the yellow liquid in 3.5–4 volumes of hot water and allowing crystallization to take place. 

    Notes: For the preparation of selenium dioxide, 200 g. (141 cc.) of concentrated nitric acid is heated in a 3-l. beaker on a hot plate under a good hood and 100 g. of selenium is added in portions of 5–10 g. A glass mechanical stirrer to break the foam hastens the process of oxidation. The resulting solution is transferred under the hood to a large evaporating dish and heated on a hot plate at a temperature not exceeding 200° until the selenious acid is completely dehydrated. The crude product is purified by sublimation. A 50-g. portion of the oxide is transferred to a 7-cm. porcelain crucible upon which is placed a 250-cc. filter flask through which a stream of cold water is run from the tap. The crucible is protected with asbestos and heated with a low flame until sublimation is complete (20–30 minutes). When the crucible has cooled, the sublimed selenium dioxide will be found wedged against the condenser. Extreme care should be used when working with selenium dioxide because of its poisonous properties. 

  8 g of 5-((5-methoxythiophen-2-yl)methyl)thiophene-2-carbaldehyde (0.0303 mol) was dissolved in 1250 ml of 95% ethanol. 0.8 g of 50% KOH solution was added under vigorous stirring.  The solution changed to deep blue.  O2 was bubled to the solution for 30 min untill blue color of the solution dissapeared.  Precipitate was filtered and crystallized in acetic acid for 2 times to give 7.3 g (Yield :88%) of ketone as needles. mp 262-263℃. 

   2.16 g of PCC(10 mmol) and 5 g of celite was added to the solution of 10,13-dimethyl-17-octyl- 2,3,4,7,8,9,10,11,12,13,14,15,16,17-tetradecahydro-1H-cyclopenta [a]phenanthren-3-yl benzoate (2 mmol) in benzene.  The mixture was refluxed for 8-15 h.  The solution was cooled to room temperature.  60 ml of ether was added.  The mixture was filtered through celite colum, washed with10 ml ether for 2 times.  Organic phase was conbined and the solvent was evapered to give ketone.