Multi-purpose thiocyanate protic ionic liquids in chemodivergent transformations of imidazolidin-2-(thi)one-based diols

Abstract

Multi-purpose thiocyanate-containing protic ionic liquids were utilised in concert as a solvent, a Brønsted acidic catalyst, and a nucleophile source for the conversion of 4,5-dihydroxy-4,5-diarylimidazolidine-2-(thi)ones into imidazo[4,5-d]oxazolethiones and imidazo[4,5-d]thiazolones. A key advantage of this process is chemoselectivity switching by tuning the electron-donating nature of aryl substituents while carefully controlling the reaction temperature. In the case of unactivated arenes, oxazolethione was forced to rearrange into thiazolone in the new highly acidic protic ionic liquid, 1-methylpyrazolium triflate. The operationally simple experimental set-up is complemented by an eco-friendly aqueous work-up/filtration procedure providing pure crystalline products.