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

Abstract

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.