强吸电子基α位的H 有较强的酸性，α碳有较强的亲核性，非常易于和醛或酮进行加成反应，生成的羟基脱水即可生成烯烃。
醛酮的加成脱水制备烯烃
强吸电子基的种类很多：硝基，氰基，酯基，醛酮。这些化合物制备烯烃的例子很容易就能用检索工具查到。
实例一
A round bottom flask was charged with NH4OAc (2.63 g, 34.1 mmol, 2.4eq) and acetic acid (20 mL). The solution was stirred until fully dissolved. To this mixture was added to nitromethane (5.98 g, 98.0 mmol, 6.9 eq) followed by 2-methylbenzaldehyde (1.71 g, 14.2 mmol, 1 eq). The flask was fitted with a reflux condenser and heated at 100 °C for six hours. The reaction was cooled to room temperature and stirred overnight. The reaction mixture was poured into distilled water (100 mL) and adjusted to pH 7 with NaOH (aq, 2M). The resulting aqueous solution was extracted with EtOAc (4 x 50 mL). The organic extracts were combined, washed with brine (1 x 100 mL), dried over Na2SO4, filtered and concentrated to a yellow-brown liquid. The crude solid was purified by flash chromatography (silica gel, 1:4 CH2Cl2:hexanes) to give the desired product (1.80 g, 78% yield) as yellow liquid.
Reference: Org. Lett. 2013, 15, 5218−5221.
实例二
The stirred mixture of Meldrums acid (0.5 g, 3.47 mmol) and anisaldehyde (0.42 mL,3.47 mmol) in water (15 mL) was heated at 75°C for 2 h. Then the reaction mixture was cooled to room temperature. The solid formed was filtered and washed with water (2×30 mL) and residue was further purified by re-crystallization from hot methanol. 2,2-Dimethyl-5-((5-methylfuran-2-yl)methylene)-1,3-dioxane-4,6-dione (1k): The compound 1k was synthesized following the general procedure A described for 1a.The compound 1k was obtained as a yellow solid (0.68 g, 83% yield).
Reference: Org. Lett., 2013, 15, 4564-4567.
实例三
2,2-Dimethyl-5-(propan-2-ylidene)-1,3-dioxane-4,6-dione (55). A reactor was charged with Meldrums acid 54 (100.0 kg, 693.8 mol, 1equiv) and acetone (500.0 kg). To the resultant solution was added morpholine(1.05 kg, 12.1 mol, 0.018 equiv) followed by AcOH (0.83 kg, 13.8 mol, 0.02 equiv). The reaction mixture was stirred at about 25 °C for about 48 h. Methylcyclohexane (385 kg) was added and acetone was distilled out under vacuum at a temperature of not more than 40 °C. MTBE (370 kg) was charged and the organic phase was washed quickly with 5% aqueous NaOH (2 × 50.0 kg). The organic phase was then distilled under vacuum at not more than 45 °C until the MTBE content was less than 5%. The slurry was cooled to about 0 °C and held at this temperature for about 1 h. The batch was filtered and the solid washed with cold (0 °C) methylcyclohexane (30.0 kg) and dried under vacuum with a nitrogen stream at 25 °C to give 55. White solid, (101.0 kg, 79% yield).
Reference:J. Org. Chem., 2013, 78,3616-3615.
实例四
A mixture of aldehyde (0.15 mmol), ketone (0.30 mmol) and catalyst I (0.03mmol) in 0.5 mL of anhydrous DMSO was vigorously stirred for 6 hr. The endpoint of the reaction was monitored by TLC. The resulting mixture was then directly purified by silica gel chromatography and fractions were collected and concentrated in vacuo to provide the product as 66% yield.
Reference: Org. Lett. 2005, 4, 601-604.
实例五
A solution of phenylacetic acid (10 mmol) in dry THF (20 mL) was added the solution of isopropyl magnesium chloride in THF (20 mmol, 1M, 20 mL) at room temperature. The resulting thick suspension was stirred at 40℃ for 1h, treated with acetone (0.87g, 15 mmol) at 25℃ during 30 min and stirred at 40℃ for 1h. Addition of a 14.2% aqueous solution of sulfuric acid (10 mL) under ice cooling, extraction of aqueous phase with Et2O (20Ml 3) and evaporation of the organic phase afford crude hydroxyl-acid as a dark oil. To a solution of the hydroxyl-acid in CH2Cl2(10 mL) was added under stirring sulfuric acid (5g) at room temperature during 2 min. CH2Cl2 was evaporated, the yellow solution was stirred for 45 min, at room temperature and then poured into ice water. The white precipitate was filtered off, washed with water, hexane and dried. The pure product was obtained by recystallization from petroleum ether/ethyl acetate.
Reference: Org.Lett. 2013,15, 3722-3725.
实例六
A round-bottomed flask equipped with a magnetic stirrer was charged with 5 g (0.03 mol) of adamantanone , 16ml (0.45 mol) of acetonitrile, and 5.04 g (0.09 mol) of granulated KOH in the presence of 10 ml of DMSO. The mixture was refluxed with stirring for 10 h. After the reaction completion, 50 ml of water was added, the mixture was cooled, the solid phase was filtered off, and product was dried and recrystallized from hexane. Yield of adamantylidene acetonitrile 5.14 g (0.03 mol, 100% yield), white crystalline substance with characteristic odor, mp 74–75°С.
Reference: Russ. J. Appl. Chem., 2013,86, 404−409.
