Organopotassium for Selective Synthesis: Potassium-Mediated anti-Borylfunctionalization of Alkynes

Organopotassium compounds, though known for over a century, have been rarely utilized in organic synthesis because of their unmanageably high reactivity. We report a reductive strategy for generation of organopotassiums from alkynes and utilization to achieve uniquely anti-selective borylfunctionalization of alkynes. The anti-diboration reaction with a bulky trialkoxyborane proceeds with broad substrate scope in a conventional flask to yield synthetically useful building blocks (E)-diborylalkenes. Flow microreactors offer precise control, enabling unsymmetrical installation of a boryl group and another functional groups in an anti fashion. Combined experimental and computational studies reveal that the potassium-induced anti-selectivity, opposite to the sodium-induced syn-selectivity, arises from the larger ionic radius of potassium cation. These findings establish a new principle for stereochemical control using abundant alkali metal elements.