Mn(III)-Catalyzed Synthesis of Pyrroles from Vinyl Azides and β-Keto Acids

Significance

Reported is the synthesis of highly substituted pyrroles through a Mn(III)-catalyzed radical-based cycloaddition. The proposed mechanism proceeds by Mn(III)-catalyzed decarboxylation to generate an α-carbonyl radical, which then undergoes reaction with the vinyl azide, forming a new carbon-carbon bond and ejecting N₂ to generate an iminyl radical. This iminyl radical then undergoes a Mn(II)-driven condensation with the remaining carbonyl to generate the desired products and regenerate the Mn(III) catalyst. Although this mechanism is presented without evidence (e.g. no indication of byproducts), each of the steps is entirely reasonable and it represents a good working hypothesis for the further utility of vinyl azides in this kind of reaction.