Pd-Catalyzed <i>ipso</i>,<i>meta</i>-Dimethylation of <i>ortho</i>-Substituted Iodoarenes via a Base-Controlled C–H Activation Cascade with Dimethyl Carbonate as the Methyl Source

Abstract

A methyl group can have a profound impact on the pharmacological properties of organic molecules. Hence, developing methylation methods and methylating reagents is essential in medicinal chemistry. We report a palladium-catalyzed dimethylation reaction of <i>ortho</i>-substituted iodoarenes using dimethyl carbonate as a methyl source. In the presence of K₂CO₃ as a base, iodoarenes are dimethylated at the <i>ipso</i>- and <i>meta</i>-positions of the iodo group, which represents a novel strategy for <i>meta</i>-C-H methylation. With KOAc as the base, subsequent oxidative C(sp³)-H/C(sp³)-H coupling occurs; in this case, the overall transformation achieves triple C-H activation to form three new C-C bonds. These reactions allow expedient access to 2,6-dimethylated phenols, 2,3-dihydrobenzofurans, and indanes, which are ubiquitous structural motifs and essential synthetic intermediates of biologically and pharmacologically active compounds.