Atom-Efficient Synthesis of Alkynylfluoroborates Using BF3 -Based Frustrated Lewis Pairs.

A sterically demanding amine, 1,2,2,6,6-pentamethylpiperidine (PMP), forms a highly reactive Lewis acid-base pair with boron trifluoride. This pair reacts with terminal acetylenes to give the products of C(sp)-H borylation, previously unknown tri- and tetraalkynylboron compounds. Trialkynylfluoroborates can serve as surrogates of alkynyltrifluoroborates for C-C coupling reactions. Using aqueous NaOH, PMP can be recovered from its tetrafluoroborate salt, which is formed as a C-H borylation byproduct. Combining the discovered borylation reactivity with the PMP recovery provides a straightforward and atom-efficient approach to synthetically useful alkynylfluoroborates.