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Tropylium Salt Promoted Hydroboration Reactions: Mechanistic Insights via Experimental and Computational Studies

preprint
submitted on 17.01.2021, 14:16 and posted on 19.01.2021, 04:24 by Nhan Nu Hong Ton, Binh Khanh Mai, Thanh Vinh Nguyen
Abstract: 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 efficiently 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 paradigm, which is triggered by a 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.

Funding

Novel organic architectures and functional materials from tropylium ions

Australian Research Council

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Organic Linchpin Reagents to Construct Structural Diversity and Complexity

Australian Research Council

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History

Email Address of Submitting Author

t.v.nguyen@unsw.edu.au

Institution

University of New South Wales, Sydney

Country

Australia

ORCID For Submitting Author

0000-0002-0757-9970

Declaration of Conflict of Interest

No conflict of interest

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