Photochemical Synthesis of Pyrazolines from Tetrazoles in Flow

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