Photoacid Catalysis

On the rise of photocatalysis in the past decades, the mild generation of free radicals by photoexcitation of transition-metal complexes and organic dyes enabling easy access to highly reactive intermediates has been developed immensely. Despite these, there are several broad-spectrum, distinct classes of small organic hydrogen bond or proton donor molecules that upon excitation with light become a powerful acidic catalyst, termed “photoacids”. Traditional acid catalysis often results in undesired side reactions due to the constant presence of the acid. However, the photoacid catalytic method significantly curtails side reactions as the acid is only temporarily present and in regulated quantities. This fleeting presence of the acid enables more controlled reaction routes, thereby reducing byproduct formation. As the acid catalyst’s generation is light-controlled, the reaction is conducted at room temperature, eliminating the need for severe chemical reagents. This prevents the breakdown of delicate substrates or intermediates. Moreover, since, the acid catalyst is produced only when and where light is applied, it minimizes side reactions and enhances the yield of the desired product. These photoacids provide better alternatives to strong metal-based Lewis acids or Brønsted acids which are air-sensitive and have limited functional group tolerability. Especially, phenol, naphthol, and thiourea molecules have been utilized as efficient organophotoacids in a limited number of organic transformations. The relevant field of photoacids in organic synthesis remained less explored. This is presumably due to the photoacids' short lifetime of the excited state. 

In line with this, our group is mainly focusing on the development of unique photoacid catalytic systems for C-C, C-O, and C-S bond formation reactions, providing rapid access to structurally functionalized molecules comprising the core structure of two or more natural products that might offer unprecedented biological applications.