Abstract
Despite 55 years having passed since the first report of the Zweifel olefination, it remains an extensively explored transition-metal-free method for the stereoselective synthesis of alkenes. The base-promoted elimination of intermediate β-iodoboronic ester 4 is a critical step in the transformation to furnish the final alkene (6) (Scheme 1). In this work, we sought to tame this highly reactive intermediate, utilising its two functional handles (alkyl iodide and boronic ester) to alter the reaction course altogether.Herein, we report our success in synthesising β-iodoboronic esters 4 in high yields from vinyl metal reagents and organoboronic esters (Scheme 1). We were able to harness the weakness of the C–I bond towards homolytic cleavage to give primary carbon-centred β-boryl radical 7. This radical underwent a thermodynamically-driven 1,2-boryl shift to furnish the more stable secondary β-boryl radical 8, which could then be trapped with a hydrogen atom transfer (HAT) reagent or a Giese acceptor to give functionalised boronic ester products 9. In this way, this protocol represents a two–carbon homologation reaction: starting boronic ester 1 is transformed to doubly homologated boronic ester 9.
| Date of Award | 21 Mar 2023 |
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| Original language | English |
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| Supervisor | Varinder K Aggarwal (Supervisor) & Craig P Butts (Supervisor) |