Manganese-Catalyzed α-Alkylation of Sulfones using Alcohols via a Hydrogen-Borrowing Strategy: Synthesis of Branched Sulfones

Herein, we report an efficient and sustainable manganese-catalyzed alpha-C-H bond alkylation methodology to synthesize branched sulfones via a hydrogen borrowing pathway. The air-stable and phosphine-free Mn-catalyst, (NNN)Mn(II)Cl2 was synthesized by using an earth-abundant, commercially available, and inexpensive precursor MnCl2.4H2O, and a stable NNN pincer i. e. [N-((benzimidazole-2-yl)methyl)quinoline-8-amine] ligand system. Taking benzyl phenyl sulfones as substrates, and benzyl alcohol derivatives as alkylating agents, a range of branched sulfones were synthesized in 40-82 % isolated yields using (NNN)Mn(II)Cl2 complex as the catalyst under open-air conditions. Control experiments and deuterium incorporation studies have also been conducted to investigate the possible reaction mechanism and to provide evidence for the hydrogen borrowing pathway. An efficient and sustainable manganese-based catalytic system has been developed for the synthesis of alpha-C-H bond alkylated (branched) sulfones using benzyl phenyl sulfones as substrate and alcohols as green and abundant alkylating agents by following the borrowing hydrogen methodology. image