无过渡金属参与甲基杂环化合物与醇的选择性有氧烯基化反应

Transition Metal-Free Selective Aerobic Olefination of Methyl N-Heteroarenes with Alcohols

采用适当的碱,在足量空气条件下,不使用任何外加催化剂即可实现甲基杂环化合物与醇的高效高选择性烯基化反应,得到烯基杂环产物.控制实验显示,醇在碱的作用下可被足量空气几乎完全氧化为羰基化合物,进而与甲基杂环化合物反应得到烯基化产物;由于存在足量空气,使用较少量的碱以及相对烷基化反应较低的温度,烯基杂环产物不能被体系中剩余的少量醇通过转移氢化还原,使得烯基化反应具有很高的选择性.因此,本方法是一种较为实用的烯基杂环化合物的合成方法,可与之前发展的少量空气下无过渡金属参与的甲基杂环化合物与醇的脱水烷基化反应形成互补.

By performing the reactions in the presence of adequate amount of air and a suitable base,selective olefination of methyl N-heteroarenes with alcohols can be effectively achieved without using any external catalyst.Control experiments revealed that,with adequate air,base can promote the aerobic oxidation of alcohols almost completely to carbonyl intermediates,which then condense with the methyl N-heteroarenes to afford the alkenyl N-heteroarene products.As the reaction is performed with adequate amount of air and a lower loading of the base at a lower temperature than that of the alkylation reaction,the generated alkenyl N-heteroarenes cannot be transfer hydrogenated to the alkylated products by the remained small amount of alcohol in the reaction mixture,which leads to a high selectivity of the olefination reaction.This method is thus a practical way for preparation of the alkenyl N-heteroarenes,being a complementary method to previous transition metal-free C-alkylation reaction of methyl N-heteroarenes with alcohols in the presence of small amount of air.