Barton–Kellogg Olefination of (CF₃S)₂C═S and Subsequent Cyclopropanation for the Installation of Bulky Bis(trifluoromethylthio)methylene Group

A protocol was developed for the large-scale preparation (nearly 200 g per batch) of (CF₃S)₂C=S. The synthesis of <i>gem</i>-bis(trifluoromethylthio)alkenes was achieved through the Barton-Kellogg reaction, without the involvement of trivalent phosphines. With slight modifications to the reaction conditions, the synthesis of <i>gem</i>-bis(trifluoromethylthio)cyclopropanes, which are difficult to obtain by other methods, can be realized. Due to the large steric hindrance of the trifluoromethylthio group, the CF₃S group may be positioned close to the <i>trans</i>-substituent rather than the <i>cis</i>-substituent in cyclopropanes, as confirmed by single-crystal X-ray analysis, contributing to unique NMR structural characteristics. Further investigation into the reaction mechanism revealed the unique reactivity of the double bond in <i>gem</i>-bis(trifluoromethylthio)alkenes.