Light-Promoted Synthesis of Glycosyl Bromides in Flow.

A new light-promoted method for the preparation of glycosyl bromides has been developed, exhibiting broad applicability to commonly used substrates. Upon irradiation with purple LEDs, bromine reacts with benzotrifluoride (PhCF3) to generate hydrogen bromide (HBr) in situ, which subsequently transforms the substrate into the glycosyl bromide in excellent yield. Unlike classical methods, the new strategy generates minimal acidic waste and features a simple workup. Notably, its scalability was demonstrated under photoflow conditions, enabling rapid, multigram-scale synthesis of glycosyl bromides. Furthermore, we show that the product bromides can be used directly as glycosyl donors in one-pot glycosylations.