Manganese-Mediated C−H Alkylation of Unbiased Arenes Using Alkylboronic Acids

The alkylation of arenes is an essential synthetic step of interest not only from the academic point of view but also in the bulk chemical industry. Despite its limitations, the Friedel–Crafts reaction is still the method of choice for most of the arene alkylation processes. Thus, the development of new strategies to synthesize alkyl arenes is a highly desirable goal, and herein, we present an alternative method to those conventional reactions. Particularly, a simple protocol for the direct C−H alkylation of unbiased arenes with alkylboronic acids in the presence of Mn(OAc)3⋅2H2O is reported. Primary or secondary unactivated alkylboronic acids served as alkylating agents for the direct functionalization of representative polyaromatic hydrocarbons (PAHs) or benzene. The results are consistent with a free‐radical mechanism. The alkylation of simple arenes, usually performed by the traditional Friedel–Crafts reaction, may also be achieved by an alternative and competitive method involving alkylboronic acids as alkylating reagents and a manganese(III) salt as promoter (see scheme).