Abstract
An intramolecular 1,2‐boryl‐anion migration from boron to carbon has been achieved by selective activation of the π system in [(vinyl)B2Pin2)]− using “soft” BR3 electrophiles (BR3=BPh3 or 9‐aryl‐BBN). The soft character is key to ensure 1,2‐migration proceeds instead of oxygen coordination/B−O activation. The BR3‐induced 1,2‐boryl‐anion migration represents a triple borylation of a vinyl Grignard reagent using only B2Pin2 and BR3 and forms differentially protected 1,1,2‐triborylated alkanes. Notably, by increasing the steric bulk at the β position of the vinyl Grignard reagent used to activate B2Pin2, 1,2‐boryl‐anion migration can be suppressed in favor of intermolecular {BPin}− transfer to BPh3, thus enabling simple access to unsymmetrical sp2−sp3 diboranes.
Highlights
The coordination of a Lewis base (LB) to diborane(4) compounds, such as B2Pin2 (1), generates an sp2-sp3 diborane in which the boron–boron bond is polarised.1 This imparts nucleophilic character to the sp2 boron, thereby enabling the mild generation of a functional equivalent of {BPin}−.1,2 This has become a powerful transition metal free methodology to borylate organic substrates and generate desirable organoboronate esters
This approach is conceptually related to the Zweifel reaction,18 but the use of borane Lewis acids and {BPin}- as the migrating group will lead to differentially functionalised 1,1,2triborylated alkanes in one step
Selective boryl-anion migration in vinyl sp2-sp3 diboranes induced by soft borane Lewis acids
Summary
Selective Boryl-Anion Migration in a Vinyl sp2sp Diborane Induced by Soft Borane Lewis Acids. Citation for published version: Fspa2ssapn3o,DVib, oCriadn, eJ,InPdrouccteedr,bRyJS, oRfot sBso,rEan&e. MJ Lewis Acids', 2018, 'Selective Boryl-Anion Migration in a Vinyl Angewandte Chemie - International Edition, vol. Selective boryl-anion migration in a vinyl sp2-sp diborane induced by soft borane Lewis acids.
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