Chemo- and site-selective aerobic oxidation of methylbenzenes to aromatic aldehydes enabled by an Fe(III) photocatalyst

We have developed a chemo- and site-selective aerobic oxidation of methylbenzenes to aromatic aldehydes. It offers several advantages, including the use of an environmentally friendly catalyst (5 ​mol% of inexpensive ferric chloride hexahydrate), the utilization of air as a green oxidant, mild conditions, scalability (up to 5 ​g scale), and operational simplicity. Furthermore, the reaction demonstrates remarkable chemo-selectivity and site-selectivity. This is evident from the lack of over-oxidation leading to carboxylic acids. Additionally, the reaction effectively converts substrates with multiple methyl groups into mono-aromatic aldehydes. The synthetic potential of this approach lies in the ability to modify complex molecules at a late stage, and conversion of inexpensive compounds into high-value fine chemicals. We expect that these characteristics will facilitate the widespread adoption of this reaction in future applications.