The direct methylation of N-heterocycles is an important transformation for the advancement of pharmaceuticals, agrochemicals, functional materials, and other chemical entities. Herein, the unprecedented C(sp2 )-H methylation of iminoamido heterocycles as nucleoside base analogues is described. Notably, trimethylsulfoxonium salt was employed as a methylating agent under aqueous conditions. A wide substrate scope and excellent level of functional-group tolerance were attained. Moreover, this method can be readily applied to the site-selective methylation of azauracil nucleosides. The feasibility of gram-scale reactions and various transformations of the products highlight the synthetic potential of the developed method. Combined deuterium-labeling experiments aided the elucidation of a plausible reaction mechanism.
Keywords: C−H functionalization; N-heterocycles; alkylation; methylation; sulfur ylides.
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