Abstract
Vinyl azides are very reactive species and as such are useful building blocks, in particular, in the synthesis of N-heterocycles. They can also serve as precursors of ketones. These form in reactions of vinyl azides with nucleophiles or radicals. We have found, however, that under light irradiation vitamin B12 catalyzes the reaction of vinyl azides with electrophiles to afford unsymmetrical carbonyl compounds in decent yields. Mechanistic studies revealed that alkyl radicals are key intermediates in this transformation.
Highlights
Vinyl azides are very reactive species and as such are useful building blocks, in particular, in the synthesis of N-heterocycles
Reactivity of Vinyl Azides transformations involve 2H-azirines as intermediates that are generated from vinyl azides under thermal, acidic, or photocatalytic conditions.[2]
These reactive species are important in the synthesis of nitrogen-containing heterocycles.[3]
Summary
The strong influence of 18-crown-6 as an additive on the reaction outcome was puzzling. Its role in the synthesis of quinolines from vinyl azides was not explained by Zhou.[17] We assumed that the complexation of reaction components, presumably an ammonium ion, could be involved To disturb this process, we performed the model reaction with the addition of KCl as 18-crown-6 exhibits a strong affinity for K+ (106 M−1 MeOH). Electrophilic alkyl bromides form C-centered nucleophilic radicals that react with electron rich alkenes exhibiting enamine-like nucleophilicity. This methodology expands the chemical toolbox of transformations for vinyl azides; their reactions with both nucleophiles and electrophiles give access to ketones.
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