Photochemical permutation of thiazoles, isothiazoles and other azoles

Thiazoles and isothiazoles are privileged motifs in drug and agrochemical discovery.^1,2 The synthesis of these derivatives is generally approached, designed and developed on a case-by-case basis. Sometimes, the lack of robust synthetic methods to a given target can pose significant difficulties or even thwart the preparation of specific derivatives for further study.^3,4 Here, we report a conceptually different approach whereby photochemical irradiation can be used to alter the structure of thiazoles and isothiazoles in a selective and predictable manner. Upon photoexcitation, these derivatives populate their π,π* singlet states that undergo a series of structural rearrangements leading to an overall permutation of the cyclic system and its substituents. This means that once the initial heteroaromatic scaffold has been prepared, it can then function as an entry point to access other molecules by selective structural permutation. This approach operates under mild photochemical conditions which tolerate complex scaffolds and chemically distinct functionalities. Preliminary findings also indicate the potential for extending this method to other azole systems, including benzo[d]isothiazole, indazole, pyrazole and isoxazole. This strategy establishes photochemical permutation as a powerful and convenient method for the preparation of complex and difficult-to-access derivatives from more available structural isomers.