已传文件：photo/1769071987.png
The main methods are as follows:
1. Corey-Fuchs reaction, proposed by Corey and Fuchs in 1972, is a simple and efficient method for converting aldehydes into alkenes. This single-carbon homologation reaction proceeds in two steps. The first step is to convert the aldehyde into a homologous dibromolefin, which is known as the Ramirez olefination reaction. The yield is typically between 80% and 90%. The second step is to treat the homologous dibromolefin with n-BuLi at 78°C. First, the first equivalent of n-BuLi undergoes a lithium-halide exchange reaction, and then the second equivalent of n-BuLi is used for the elimination reaction to obtain the alkene.
2. Seyferth-Gilbert reagent: Dimethoxyphosphoryl azide methane (MeO)₂P(O)CHN₂. The operation is relatively dangerous (azo compounds). Modern improved version/ best choice: Bestmann-Ohira reagent (dimethoxyphosphoryl azidomethylphosphonic acid dimethyl ester) (MeO)₂P(O)C(N₂)PO(OMe)₂ or its analogues. It is safer, more stable, and readily available in commercial form. Reaction conditions: In alcohols (such as methanol, tert-butanol), catalyzed by weak bases (such as K₂CO₃, Cs₂CO₃).
3. Colvin rearrangement reaction. After the reaction between aldehyde-ketone and LiTMSD (trimethylsilyl azide methane lithium salt), elimination and deamination occur to obtain the carbene, and then the rearrangement proceeds to form an alkyne with one more carbon.
