Synthesis of new thioxanthenes by organocatalytic intramolecular Friedel-Crafts reaction

Abstract

An efficient organocatalytic route has been developed to synthesize novel substituted thioxanthenes (2a-2v) starting from diaryl thioether alcohols (1a-1v) using the intramolecular Friedel-Crafts reaction. The starting materials were obtained in two stages via a coupling reaction followed by the Grignard reaction. In this study, we tried for the first time to use some organic BrOnsted acids as organocatalysts (3a-3h) in the intramolecular Friedel-Crafts cyclization reaction of thioether alcohols. The synthesis of original substituted thioxanthenes was achieved within 15minutes by using N-triflylphosphoramide (3h) with quantitative yields in THF at room temperature.