Metal-Free Divergent Hydroboration/Multiboration of Terminal Alkynes via Markovnikov Pathway.

Hydroboration/multiboration of alkynes has been considered a straightforward route for the construction of high-value alkenylboronates and multiborylalkanes, especially reflected by the productions of β-alkenylboronates and related multiborylalkanes based on the anti-Markovnikov-type transformations of terminal alkyne. However, the syntheses of branched α-alkenylboronates and related multiborylalkanes remain elusive due to the thermodynamically and kinetically unfavorable Markovnikov hydroboration process. Herein, we present a conceptually novel metal-free approach for Markovnikov hydroboration of terminal alkynes to achieve the α-alkenylboronates. Derived from it, we have successfully realized unprecedented tailor-made multiborations (2,2-dihydroboration, 1,2,2-triboration, and 1,2-dihydroboration) of alkynes by simply changing the proton sources and solvents. The broad substrate scope and outstanding chemo- and regioselectivities of the developed approaches unlock opportunities to exploit these formerly unattainable organoboronates, thereby expanding uncharted chemical space. The preliminary mechanistic studies highlight the synergistic roles of amide solvents, suitable proton sources, and Bcat in facilitating these tunable transformations.