羧酸与胺的缩合酰化反应 ：羧酸与胺的反应是合成酰胺的重要方法。由于这一反应是一个平衡反应，因此采 用过量的反应物之一或除去反应中生成的水， 均有利于平衡向产物方向转移。除去水 的方法通常是在反应物中加入苯或甲苯进行共沸蒸馏。
例如将α-羟基乙酸及苄胺于 90℃共热， 并蒸出生成的水及过量的苄胺，则生成α羟基乙酰基苄胺。
1.1 应用氯甲酸乙酯或异丁酯活性酯法合成酰胺示例 1.1 应用氯甲酸乙酯或异丁酯活性酯法合成酰胺示例
活性酯法早期主要应用酸与氯甲酸乙酯或异丁酯反应生成混合酸酐，而后再与胺反 应得到相应的酰胺，这一反应如果酸的α-位位阻大或者连有吸电子基团，有时会停留在 混合酸酐这一步，但加热可以促使其反应；这一反应也可用于无取代酰胺的合成。
应用羰基二咪唑(CDI)与羧酸反应得到活性较高的酰基咪唑，许多酰基咪唑有一定的稳定性，有时可以分离出来，但一般来说其不用分离，反应液直接与胺一锅反应制备相应的酰胺；有文献报道羰基二咪唑与三氟甲磺酸甲酯反应得到的二甲基化的三氟甲磺 酸盐(CBMIT)的缩合性能更好。该类反应由于过量的 CDI 或 CBMIT 会和胺反应得到脲 的副产物，因此其用量一定要严格控制在 1 当量。近我们发现应用 CDI 合成 Weinreb 酰胺是一个较好的方法。
常用的磺酰氯有甲烷磺酰氯（MsCl），对甲苯磺酰氯（TsCl）和对硝基苯磺 酰氯（NsCl）, 对硝基苯磺酰氯由于其吸电子性，其与酸反应生成活性更高的混合酸酐， 一般二级胺和三级胺，甚至位阻很大的胺都能顺利反应。
通过酸与 Boc 酸酐反应得到的混合酸酐与氨反应可得到相应的伯酰胺。
A solution of acid 1 and 4-methylmorpholine (NMM, 0.54 mL, 4.92 mmol) in DMF (10 mL) was treated at room temperature with isobutyl chloroformate (0.64 mL, 4.92 mmol). After 30 min, pentylamine (0.57 mL, 4.92 mmol) was added. The reaction mixture was stirred for 12 h. The solvent was evaporated, and the residue was partitioned between ethyl acetate (25 mL) and water (25 mL). The ethyl acetate layer was washed with 5% NaHCO3 (10 mL) and brine (20 mL), dried over Na2SO4, and evaporated. The residue was chromatographed on silica gel eluting with hexane and ethyl acetate (2:1) to give 0.33 g (33%) of tert-butoxycarbonylated amino amide (2).
To a cooled (-20℃) solution of compound 3 (4.8 g, 18 mmol) in anhydrous THF (50 mL) was added Et3N (2.5 mL, 18 mmol) during 20 min. After 10 min ethyl chloroformate (1.7 mL, 18mmol) was added at the same temperature during 10 min and stirred for an additional 20 min. The resulting mixture was saturated with NH3 gas and kept at r.t. overnight. The mixture was concentrated at reduced pressure, the residue was diluted with H2O (10 mL) and extracted with EtOAc (4 *10 mL). The combined organic phases were dried (Na2SO4), filtered and concentrated to afford a white solid. It was recrystallized from petroleum ether and ethyl acetate to afford pure product 4 as white crystal (3.1 g, 65%).
To acid 5 (4.0 g, 14.1 mmol) in CH2Cl2 (70 mL) at 23℃ was added 1, 1’-carbonyldiimidazole (3.65 g, 22.5 mmol) in equal portions over 15 min. After the final addition, stirring was continued for 10 min, then N,O-dimethylhydroxylamine • HCl (3.43 g, 35.16 mmol) was added in one portion. The reaction was allowed to stir at 23℃ for 3 h. Et2O was added (50 mL) and the reaction mixture was filtered. The filtrate was evaporated, diluted with Et2O (125 mL), washed with 5% aq. citric acid (2 x 50 mL) and brine (50 mL), and dried over MgSO4. The crude product was purified by flash chromatography (3:1 hexanes: EtOAc) to afford Weinreb amide 6 (4.29 g, 93% yield) as a colorless oil. Rf 0.42 (2:1 hexanes:EtOAc); 1H NMR (300 MHz, CDCl3): δ 5.43 (m, 1H), 4.72 (s, 1H), 4.17-4.11 (m, 1H), 3.71 (s, 3H), 3.22 (s, 3H), 2.59-2.24 (comp. m, 3H), 2.03 (dd, J = 14.6 Hz, 4.1 Hz, 1H), 1.75-1.71 (m, 3H), 0.86 (s, 9H), 0.11 (s, 3H), 0.09 (s, 3H).
A mixture of the benzoic acid (10 mmol), 4-methylbenzene-1-sulfonyl chloride (10 mmol), K2CO3 (5.52 g, 40 mmol) and TEBAC (0.23 g, 1mmol) in 60 mL of benzene is stirred at reflux for 40 min. Then ethyl 2-aminoacetate (10 mmol) is added and stirring is continued for 10 min at reflux temperature. The precipitate is filtered off, and the filtrate is evaporated under reduced pressure. The carboxamide 8 thus obtained is crystallized from MeOH to afford the pure product (yield 82%).
To a stirred solution of N-protected amino acid 9 (10 mmol), pyridine (0.5 ml) and Boc2O (3 g, 13 mmol) in an appropriate solvent (such as dioxane, DMF and CH3CN, 10-15 ml), ammonium hydrogencarbonate (1 g, 12.6 mmol) was added and the mixture was stirred for 4-16 h. Ethyl acetate was added and after washings with water and 5% H2SO4, the solution was dried, the solvent was evaporated and the product was triturated with ether. In another variant the reaction mixture was diluted with water (30-40 ml), stirred until crystallization was completed, a residue was then collected by filtration, washed by water, dried and recrystallized as necessary.