Friedel-Crafts酰基化反应

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Friedel-Crafts酰基化反应

在Lewis酸催化下利用酰卤或酸酐在芳基或脂肪基底物上引入酮基的反应称为Friedel-Crafts酰基化反应。

反应机理为：第一步是一当量的Lewis酸和酰化试剂络合，然后另一分子的Lewis酸继续络合形成一个正负电子分离的中间体，其可以在离子化试剂中分解为酰基正离子。通过典型的SEAr机理形成芳基酮-Lewis酸络合物，其脱掉卤化氢生成芳基酮产物。

反应特点：1）芳环上含有富电子取代基 (R1 = -OH, -NR2, alkyl,etc.) 的酰基化产率较高；2）有强吸电子基团 (R1 = -NO2, -CX3, etc.) 的芳香底物和一些杂环化合物（如吡啶，喹啉）不能发生酰基化反应，因此可以当做溶剂（但这些惰性底物可以通过Minisci反应进行酰基化）；3）酰化试剂除了酰氯，还有芳基和脂肪羧酸，酸酐，烯酮，酯和多酰卤试剂（草酰卤）；4）酰卤的活性顺序为：I >Br > Cl > F；5）与烷基化不同，酰基化的催化剂量要稍微多余一个当量，因为酰基化试剂本身要络合一倍当量的催化剂，多出的才是有效的催化剂；6）常用的催化剂有：AlX3，三幅甲磺酸的镧系金属盐，分子筛，质子酸 (e.g., H2SO4, H3PO4)，FeCl3,ZnCl2, PPA；7）在高活性酰化试剂（如酰基三氟甲磺酸酐）或强富电子的底物发生反应时可能需要很少或不需要催化剂；8）酰基化反应不会得到多酰基化产物，因为反应生成第一个酰基取代物时，底物就会钝化不再往下进行；9）酰基化反应很少发生重排，因此用于制备直链烷基取代芳基化合物（先酰化再还原）；10）含有未保护的Lewis碱基团（如氨基）的底物，发生反应时，酰基化试剂会优先和这些基团反应；11）分子内的Friedel-Crafts酰基化反应可以容易关5-,6- 和7-元环。此反应的一个缺点是Lewis酸催化剂在反应后处理时会破坏，不能回收，然而近期研究表明多相催化剂（主要是分子筛）在工业级生产中是可行的。

反应实例：


参考文献：

Strategic Applications of Named Reactions in Organic Synthesis, László Kürti and BarbaraCzakó, Friedel-Crafts acylation. page 176-177.



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