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 gem-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 gem-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 trans-substituent rather than the cis-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 gem-bis­(trifluoromethylthio)­alkenes.