Assembly and Application of a Low Budget Photoreactor **

Photochemistry is a fast growing research field and many transformations previously not accessible to chemists now have become part of an ever growing standard repertoire. The limiting factors for a photoreactor system however are the possibility to perform stirring, removal of excess heat and the irradiation with UV or visible light – all that within a secure surrounding. Systems for starters may be as expensive as several thousand Euro. Here we design and assemble a LED photoreactor using scrap and standard materials, spending less than 30 € for a LED. The system may be adjusted to any required wavelength and its assembly is shown for the use of a 400 nm LED. To demonstrate its application, we then exemplarily use the reactor in the removal of a photolabile protection group during the synthesis of a SARS‐CoV‐2 spike protein glycopeptide.