5 、其它缩合剂
三苯基磷-多卤代甲 1997,6489)、三苯基磷-NBS(Tetrahedron lett. 1997,5359)等也可以用于酰胺的缩合。另外，当分子内有多个羧基存在时，有文献报道使用三（2，6-二甲氧基苯基）铋作缩合剂可选择性的将连接到伯碳原子上的羧基缩合为酰胺，而连接在仲碳和叔碳上的羧基 则不反应。
5.1 应用三苯基磷-多卤代甲烷合成酰胺示例
2 mmol of a carboxylic acid 37, 2 mmol of an amine 38, 2 mmol of triethylamine, and 2 mmol of carbon tetrabromide are dissolved in 5 mL of dry methylene chloride. Solid triphenyl phosphine (2 mmol, 554 mg) is then added portionwise over 5 min to the solution stirred at room temperature. After a further period of 10 min., the solvent is evaporated, and a 1:1 mixture of hexane and ethyl acetate is added. The solid triphenyl phosphine oxide is filtered off, the solvents are evaporated and the crude material can be purified by conventional methods.
5.2 应用三苯基磷-六氯丙酮合成酰胺示例
A mixture of benzoic acid (122 mg, 1mmol) and hexachloroacetone (132 mg, 0.5 mmol) in methylene chloride (2 mL) was stirred under argon and cooled down to -78℃. Triphenylphosphine (262 mg, 1 mmol) in methylene chloride (1 mL) was added dropwise and the mixture was stirred for 20 min. The acyl chloride solution was then treated with a solution of benzylamine (107 mg, 1 mmol) in methylene chloride (1 mL) dropwise, followed by triethylamine (101 mg, 1mmol) in methylene chloride (1 mL) the reaction mixture was then allowed to reach room temperature after which the solvent was evaporated under high vacuum. The dry residue was suspended in 20% ethyl acetate in hexane (4 mL) and silica gel added in order to obtain pasta. This pasta was added onto the top of a silica gel column and the elution performed with the same solvent. The pure fractions provided the title compound as a white solid (187 mg, 95%): m. p. 102℃.
5.3 应用三苯基磷-NBS合成酰胺示例
To a stirred solution of triphenylphosphine (2.55 mmol, 0.67 g) and hexanoic acid (2.5 mmol,0.29 g) in anhydrous dichloromethane (5 ml) at 0℃ was added N-bromosuccinimide (NBS, 2.8 mmol, 0.50 g) in one portion. The reaction mixture containing 0.25 mmol of 40 was thereafter set aside at room temperature while a new solution was being prepared: 3-Aminophenol (2.5 mmol, 0.28 g) and pyridine (3.20 mmol, 0.26 g) was dissolved in THF (5 ml). The mixture was cooled to about -25℃ (ethanol/granular CO2), and vigorously stirred while the ready-made solution of 40 was added dropwise. The cooling bath was removed after a few min and the temperature allowed to rise towards room temperature. Most of the solvents were removed under reduced pressure and the product purified by flash chromatography on Merck No. 9385 silica gel 60, using ether as eluent. Removal of the solvent gave N-(3-hydroxyphenyl)-hexanamide 41 (0.52 g, 98 %) as a colourless solid, m.p. 139-140℃. 1H NMR (200 MHz, acetone-d6): δ 0.90 (m, 3H, CH3), 1.35 (m, 4H, CH2), 1.65 (m, 2H, CH2), 2.35 (t, 2H, CH2), 6.52 (m, IH, H ~o,~), 7.0 (m, 2H, H~om.), 7.42 (s, 1H, H~o), 8.4 (s, 1H, OH), 9.05 (s, 1H, NH); MS (70 eV): m/z(%) 207 (17, M+), 151 (6.5), 109 (100).
