Highly Active Cooperative Lewis Acid—Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones

Enantiopure secondary alcohols are fundamental high-value synthetic building blocks. One of the most attractive ways to get access this compound class is catalytic hydroboration. We describe a new concept for reaction type that allowed exceptional turnover numbers (up 15 400), which were increased by around 1.5–3 orders magnitude compared active catalysts previously reported. In our an aprotic ammonium halide moiety cooperates with oxophilic Lewis acid within same catalyst molecule. Control experiments reveal both centers essential observed activity. Kinetic, spectroscopic and computational studies show hydride transfer rate limiting proceeds via concerted mechanism, in at Boron continuously displaced iodide, reminiscent SN2 reaction. The catalyst, accessible high yields few steps, was found be stable during catalysis, readily recyclable could reused 10 times still efficiently working.