The Selective<i>N</i>-Monoalkylation of Amides with Alkyl Halides in the Presence of Alumina and KOH
作者:Kazuaki Sukata
DOI:10.1246/bcsj.58.838
日期:1985.3
The effects of alumina impregnated with KOH (KOH/Al2O3) and a mixture of alumina and powdered KOH (KOH+Al2O3) have been examined using the alkylation of benzamide under various conditions. In each case, alkylation occurs exclusively in the pores of the alumina, the extent depending upon the alumina-pore size. For both yield and selectivity for N-monoalkylation, KOH+Al2O3 is superior to KOH/Al2O3. Dioxane is the best of the solvents employed. It is proposed that, in dioxane, an enolate-like species, (Remark: Graphics omitted.), exists as stable ion-pair aggregates, which are the true reactants in the pore. This method, using KOH/Al2O3 or KOH+Al2O3, has been applied to N-alkylation of the other amides, giving the N-monoalkylated products in substantial yields with extremely high selectivities. 2-Phenylacetamide is regioselectively N-monoalkylated in high yields. This regioselectivity is explained in terms of steric hindrance.
使用KOH浸渍的氧化铝(KOH/Al2O3)和氧化铝与粉末状KOH的混合物(KOH+Al2O3),在不同条件下研究了苯甲酰胺的烷基化反应。在每种情况下,烷基化反应仅在氧化铝的孔隙中发生,其程度取决于氧化铝的孔径大小。对于N-单烷基化的产率和选择性,KOH+Al2O3优于KOH/Al2O3。二氧六环是所使用溶剂中最好的。研究表明,在二氧六环中,类似于烯醇盐的物种(注:图形省略)以稳定的离子对聚集形式存在,这些是孔隙中的真正反应物。这种方法使用KOH/Al2O3或KOH+Al2O3,已应用于其他酰胺的N-烷基化,以极高的选择性获得了大量的N-单烷基化产物。2-苯基乙酰胺以高产率选择性地进行N-单烷基化。这种区域选择性可通过空间位阻来解释。