Modular synthesis of 1,2-azaborines via ring-opening BN-isostere benzannulation

21 March 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

1,2-Azaborines represent a unique class of benzene isosteres that holds great potential for various applications. However, it remains a long-standing challenge to prepare monocyclic 1,2-azaborines in an efficient and modular manner. Here we report a straightforward method to directly access diverse multi-substituted 1,2-azaborines from readily available cyclopropyl imines/ketones and dibromoboranes under relatively mild conditions. The reaction is scalable, shows a broad substrate scope, and tolerates a range of functional groups. The utility of this method is demonstrated in the concise syntheses of BN isosteres of a PD-1/PD-L1 inhibitor and pyrethroid insecticide bifenthrin. Combined experimental and computational mechanistic studies suggest that the reaction pathway involves boron-mediated cyclopropane ring-opening and base-mediated elimination, followed by an unusual low-barrier 6π-electrocyclization accelerated by the BN/CC isomerism.

Keywords

azaborines
modular synthesis
6π-electrocyclization
BN isosteres

Supplementary materials

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Title
Modular synthesis of 1,2-azaborines via ring-opening BN-isostere benzannulation
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Supplementary information containing detailed experimental data, spectra, figures, etc.
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