A Remarkable Influence of a Trifluoromethyl Group on the Reactions of β-Mercaptoalcohols with Fluorinated α-Bromoenones

Isomeric fluorinated α‐bromoenones react with dinucleophilic β‐mercaptoalcohols in CH 2 Cl 2 at room temperature in the presence of Et 3 N in a multistep process. Depending on the position of the CF 3 group, different O,S ‐heterocycles or non‐cyclic products were obtained. With 3‐bromo‐1,1,1‐trifluorobut‐3‐en‐2‐ones derivatives of 1,4‐oxathianes were formed, but isomeric 2‐bromo‐4,4,4‐trifluorobut‐2‐en‐1‐ones yielded 1,3‐oxathiolanes or non‐cyclic sulfides. The thia‐Michael addition is proposed as the initial step of the reaction, and the final heterocyclization is governed by the location of the CF 3 group.