New fused dithiabicyclic compounds from the reaction of N,N-dialkyl perfluorothioamides with allylmagnesium halides

Allylmagnesium reagents react with N,N-dialkylperfluorothioamide to give, at low temperature, an adduct stable enough to be trapped. At room temperature, this adduct can evolve by elimination of either a sulfide salt, leading to an iminium intermediate, and then an N,N-dialkyl-α,α-bis(allyl)-α-perfluoroalkylamine. This process is favoured if an excess of allyl magnesium is used. Alternatively, the adduct eliminates an aminyl moiety giving allyl(perfluoroalkyl)thioketone which is converted in situ into an unprecedented fused bis(perfluoroalkyl) bis(dihydrothiopyrane). A sequence deprotonation of the thioketone – oxidation of the resulting dienethiolate – dimerization of the dienethiyl radical is proposed to rationalize the formation of this unexpected bicyclic compound.