| Autor: |
Ton NNH; School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia., Mai BK; Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States., Nguyen TV; School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia. |
| Abstrakt: |
Hydroboration reaction of alkynes is one of the most synthetically powerful tools to access organoboron compounds, versatile precursors for cross-coupling chemistry. This type of reaction has traditionally been mediated by transition-metal or main group catalysts. Herein, we report a novel method using tropylium salts, typically known as organic oxidants and Lewis acids, to promote the hydroboration reaction of alkynes. A broad range of vinylboranes can be easily accessed via this metal-free protocol. Similar hydroboration reactions of alkenes and epoxides can also be efficiently catalyzed by the same tropylium catalysts. Experimental studies and DFT calculations suggested that the reaction follows an uncommon mechanistic pathway, which is triggered by the hydride abstraction of pinacolborane with tropylium ion. This is followed by a series of in situ counterion-activated substituent exchanges to generate boron intermediates that promote the hydroboration reaction. |
