Organocatalytic hydroboration of olefins in pyrrolidinium ionic liquids

Abstract

An efficient, simple, metal and ligand free, regioselective hydroboration of alkenes has been developed using pinacolborane (HBpin) as a reducing reagent and 1-ethyl-methylpyrrolidinium triflate [EMPyrr][OTf] as a non-corrosive and recyclable organocatalyst. The described protocol is scalable and compatible with a variety of alkenes offering the desired organoboron compounds in moderate-to-excellent yields. The system was reused in 30 cycles with comparable effectivity and stable selectivity of the process, increasing its sustainability. The utility of the obtained alkylboronates was checked in various subsequent transformations such as Suzuki–Miyaura coupling, Zweifel olefination and oxidation. Moreover, a reaction mechanism based on previously reported literature and NMR studies was proposed.