Trifluorination of 1,1-Diarylethenes Using Selectfluor/HF Reagent and Experimental Evidence for a Single Electron...

A direct trifluorination reaction was discovered to synthesize 1,1-diaryl-1,2,2-trifluoroethanes from 1,1-diarylethenes. A very simple procedure using Selectfluor/pyr·9HF reagent under mild conditions afforded high yields of the trifluorides. For substrates bearing electron-donating methoxy or methyl groups at the para position, the yields were improved by selecting the appropriate amine·HF reagent. The trifluoride was confirmed to be produced by first generating 1,2-difluoro-1,1-diphenylethane, followed by HF elimination to generate 2-fluoro-1,1-diphenylethene, which was then finally difluorinated. Previous radical clock and cyclopropyl motif experiments had not demonstrated the existence of a radical cation intermediate. However, the fluorination of substrates bearing 2-(methylthio)phenyl and 2-(phenylthio)phenyl groups experimentally demonstrated the existence of radical cation species.