化学化学方法将醛或酮的羰基直接转化为亚甲基有如下几种：1) Clemmensen 还原;2) Wolff-Kishner-黄鸣龙还原; 3) LiAlH 4 -AlCl3  法; 4) NaBH 4 -CF3CO2H 法; 5) Et3SiH-BF3 or CF3CO2H法; 6) HI-Phosphorus 法；7) 催化氢化法 .
      催化氢化转化羰基为亚甲基由Brieger报导，他们使用Pd/C作为催化剂，并用FeCl 3 作Lewis酸促进剂. 另外,有综述专门提到用甲酸铵作催化氢化转移剂.

     近期,哈佛的Andrew Myers 在其关于腙衍生物工作中报导了用Sc(OTf) 3 作催化剂的有效的低温Wolff-Kishner还原.

     对于有些结构复杂，带有多种敏感官能团时，以上这些一步或一锅法无法将醛或酮的羰基直接转化为亚甲基，因此可能需要将醛或酮转化为其他官能团进行除去。较为常见的方法是转化为醇羟基除去（醇羟基除去方法见脱羟基反应部分）；另外，可以将醛或酮转化为乙二硫醇的缩醛或酮，再用 Raney Ni 氢化还原为亚甲基；另外也有文献将醛或酮转化为对甲苯磺酰肼的腙，再用 DiBAL 或 NaBH(OAc)3 还原。

Clemmensen 还原

      将醛或酮用锌汞齐处理在浓盐酸下加热可以将醛或酮的羰基转化为亚甲基. 这就是克莱门森（Clemmensen）还原  . 很明显,对酸敏感的底物（醛酮）不能使用此法还原（如醇羟基、C=C等）。

     此法对于还原芳香酮和双烷基酮有一定的通用性。其用在还原芳香酮是间接在芳环上引入直链烃基的方法之一。

反应机理

      反应发生在锌催化剂表面. 由于将相应的醇用于此反应条件并不能得到亚甲基化合物,因此该反应中间态可能没有醇产生. 下图大致描述了克莱门森（Clemmensen）还原的机理.

Clemmensen 还原芳基酮示例

     Amalgamated zinc is prepared by shaking for five minutes a mixture of 120 g. of mossy zinc,12 g of mercuric chloride, 200 mL of water, and 5–6 mL of concentrated hydrochloric acid contained in a 1-L round-bottomed flask. The solution is decanted and the following reagents are added, in the order named, to the zinc: 75 mL of water, 175 mL of concentrated hydrochloric acid, 100 mL of toluene, and 50 g (0.28 mol) of β-benzoylpropionic acid. The flask is fitted with a vertical condenser connected to a gas absorption trap, and the reaction mixture is boiled vigorously for twenty-five to thirty hours. Three 50 mL portions of concentrated hydrochloric acid are added at approximately six-hour intervals during the refluxing period. After cooling to room temperature the layers are separated. The aqueous layer is diluted with 200 mL of water and extracted with three 75 mL portions of ether. The toluene layer and the ether extracts are combined, washed with water, and dried over calcium chloride. The solvents are removed by distillation under reduced pressure on the steam bath, after which the χ-phenylbutyric acid is distilled at 178–181°/19 mm. (148–154°/8–10 mm., 125–130°/3 mm.). The yield of acid, which melts at 46–48°, is 38–41 g. (82–89%).

Clemmensen 还原二烷基酮示例

     Clemmensen reduction of methyl 8,8,8-trifluoro-4-ketooctanoate was carried out in a 2-liter, three neck, round-bottom flask fitted with a Liebig condenser surmounted by a Friedrichs condenser, a Hershberg stirrer with a Trubore bearing, and a 50-mL dropping-funnel. The condensers were sealed with a Dry-Ice trap, and a gas washing bottle filled with petroleum ether (65-110 o C). The flask was charged with 300 g. of amalgamated, reagent grade, mossy zinc, 100 mL of water, 240 mL of concentrated hydrochloric acid, and 93.0 g (0.41 mole) of methyl 8,8,8-trifluoro-ketooctanoate. The mixture was heated with an oil-bath at 120-130℃. The reactiori was continued for 112 hours, and an additional 50 g. of amalgamated zinc and 50 mL of concentrated hydrochloric acid were added every 24 hours. The reaction mixture was extracted with four portions of isooctane, and then the extract was washed with water and dried by azeotropic distillation with ethylene chloride. Fractional distillation of the residue through a Vigreux partial take-off, fractionating column yielded two main fractions: ω-trifluorooctanoic acid, 31.6 g. (72%, converted keto acid), b.p. 129 o C (10 mm.);and 8,8,8-trifluoro-4-ketooctanoic acid, 36.0 g., b.p. 136 ℃