Photochemical Synthesis of Pyrazolines from Tetrazoles in Flow

Adam Burke^a, Silvia Spiccio^a, Mara Di Filippo^a, Marcus Baumann^b

• ^aChemistry, University College Dublin, Dublin, Ireland
• ^bChemistry, University of Durham, Durham, United Kingdom of Great Britain and Northern Ireland

Pyrazolines and their pyrazole congeners are important heterocyclic building blocks with numerous applications in the fine chemical industries. However, traditional routes towards these entities are based on multistep syntheses generating substantial amounts of chemical waste. Here we report an alternative approach using UV-light to convert tetrazoles to pyrazolines via a reagent-free photo-click strategy. This route generates nitrile imine dipoles in situ that are trapped with different dipolarophiles rendering a selection of these heterocyclic targets in high chemical yields. A continuous flow method is ultimately realized that generates multi-gram quantities of product in a safe and readily scalable manner thus demonstrating the value of this photochemical approach for future exploitations in industry.

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