Efficient scale up of photochemical bromination of conjugated allylic compounds in continuous-flow

A continuous-flow process for the bromination of conjugated allylic compounds with N-bromosuccinimide (NBS) is developed. The reaction was optimized in a self-made continuous-flow photoreactor based on a commercially available household lamp. The productivity of this continuous step attains 70.5 g/h under the optimal conditions. Compared to batch-mode synthesis, the conversion rate and selectivity of this flow-mode was significantly improved. In addition, the reaction time could be significantly reduced from a few hours to a few minutes.