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 Brønsted acids as organocatalysts (3a–3h) in the intramolecular Friedel–Crafts cyclization reaction of thioether alcohols. The synthesis of original substituted thioxanthenes was achieved within 15 minutes by using N-triflylphosphoramide (3h) with quantitative yields in THF at room temperature.

Graphical Abstract

Keywords:

• Brønsted acid catalyst
• Friedel–Crafts reaction
• intramolecular cyclization
• N-triflylphosphoramide
• thioxanthenes

Supplementary information

Experimental details, analytical data for all compounds and copies of ¹H NMR, 13C NMR spectra, GC-MS and elemental analysis are provided.

Acknowledgments

This work was supported by Istanbul University, Scientific Research Projects, project number BYP-2017-24039.

Disclosure statement

No potential conflict of interest was reported by the author.