Direct functionalization of C-H bonds reduces the number of synthetic steps for a target molecule enhancing efficiency and avoiding undesired waste material. Iridium catalyzed C-H activation-borylation (CHB) is now an established method to access aryl boronic esters. Regioselectivity challenges can arise when multiple hydrogens are present in the molecule. CHB are traditionally directed by sterics yielding a mixture of meta and para products for monosubstitued arenes. Reactions that produce exclusively the meta or para regioisomer are more challenging. This presentation will show a method to direct para CHB via ion-pair electrostatic interactions of sulfated phenols, benzyl alcohols and anilines with bulky countercations. It is proposed that the tetraalkylammonium cation shields the meta position, while leaving the para accessible. The effects of additional/different substituents, ligands, additives, and chain length of the tetraalkylammonium on regioselectivity will be discussed.

Para selective iridium catalyzed C-H borylation of sulfates and sulfamates directed by ion-pair electrostatic interactions

ACS Fall 2020 Virtual Meeting

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