Light-Driven Flow Reaction Features Molecular Acrobatics

By shining ultraviolet light on solutions of alkene-substituted pyrroles, chemists have enticed the molecules to perform never-before-seen molecular acrobatics. Through a twisting and turning cycloaddition-rearrangement reaction, simple pyrroles yield complex tricyclic aziridines. The reaction could be a boon for natural product and small-molecule drug synthesis (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201208892). Photochemistry is usually simple, efficient, inexpensive, and catalyst-free. Plus, in a single step it often leads to products with molecular complexity that can’t be matched without many steps in a conventional synthesis. Katie G. Maskill, Kevin I. Booker-Milburn, and coworkers at the University of Bristol, in England, found that by irradiating various N-butenylpyrroles in acetonitrile with 254-nm light they can produce batches of tricyclic aziridines in yields of up to 60%. Booker-Milburn’s group had previously developed a continuous-flow reactor for scaling up photochemical reactions. In the new work, the team used a modified version of the reactor to make the aziridines, such as the one shown, at a rate of about 1 g per hour. That scale is difficult to achieve with batch photochemical reactions.