Photochemical Aerobic Synthesis of para-Quinols in Continuous Flow Mode

The development of a simple and robust continuous flow method for the aerobic photooxidation of phenols is reported. This approach is attractive as it uses ambient air which is the source of the singlet oxygen required in this transformation. Methylene blue is used in an aqueous solvent system in combination with either green or red LEDs. While the latter LED option is advantageous due to its lower energy consumption, both approaches afford the desired para-quinol products in good yields after reduction of the para-peroxyquinol intermediates. The use of air at atmospheric pressure, along with low-energy LED sources and a benign solvent system render this flow method an attractive and easy to implement strategy for the generation of para-quinol products as valuable chemical building blocks.