Photochemical Flow Synthesis of Trisubstituted Oxazoles Enabled by High-Power UV-B LED Modules.

The use of a newly developed UV-B LED module for the continuous flow synthesis of a variety of trisubstituted oxazole products from readily available isoxazoles is reported. Crucially, this work demonstrates for the first time that these UV-LED modules (up to 40 W electrical power) are effective replacements of classical medium-pressure Hg-lamps by providing monochromatic light (centered at 308 nm) which facilitates the highlighted photochemical process. The desired oxazole products are afforded in high yields, and the applicability toward synthesizing analogs of the anti-inflammatory drug oxaprozin at multigram scale is reported. The availability of such high-power UV-LED modules not only circumvents the use of inefficient metal vapor lamps but also highlights new opportunities for light-driven processes in general.