LAUSR

Selective creation of quaternary carbon centers has been a long-standing challenge in synthetic chemistry. We report here the chromium-catalyzed, para-selective formation of arylated quaternary carbon centers by alkylative reactions of benzamide derivatives with tertiary alkylmagnesium bromides at room temperature. The reaction, which was enabled by a low-cost chromium(III) salt combined with trimethylsilyl bromide, introduces a sterically bulky tertiary alkyl scaffold on the para-position of benzamide derivatives in a highly selective fashion without either isomerization of the tertiary alkyl group or formation of ortho-alkylated byproducts. Forming low-valent Cr species in situ by reaction of CrCl3 with t-BuMgBr accompanied by evolution of hydrogen can be considered, which serves as reactive species to promote the reaction. The para-alkylation likely occurs via a radical-type nucleophilic substitution of imino-coordination benzimidate intermediate.The selective installation of quaternary carbon substituents on arenes is a highly challenging synthetic goal. Here, the authors report a chromium-catalyzed para-selective functionalization of benzamides with tertiary organometallic reagents under mild conditions.