Simple Protocol for Preparation of Diels-Alder Adducts of Perfluorinated Thioketones

Abstract A simple procedure for the preparation of new Diels-Alder adducts of perfluorinated thioketones is reported. The corresponding adducts were prepared in 30-78% yield by reaction of alicyclic perfluorinated olefin, sulfur, diene and CsF catalyst. While the synthesis of quadricyclane, cyclohexadiene-1,3, cycloheptatriene-1,3,5 and 2,3-dimethylbutadiene-1,3 adducts was straightforward, a modified protocol was used in the case of the reaction of cyclopentadiene-1,3, F-pentene-2 and sulfur in order to avoid the formation of cycloadduct of cyclopentediene and F-pentene-2. In this case the olefin first was reacted with sulfur and cyclopentadiene was added later. In separate experiments it was demonstarted that the reaction of F-pentene-2, sulfur and CsF catallyst leds to the formation of two isomeric perfluorinated 1,3-dithiolanes along with equimolar amount of branched polysulfides (R f ) 2 S x . Due to broadening of signals in 19 F NMR spectra of the most cycloadducts, additiononal variable temperature NMR experiments were carried out, and rotational barriers several adducts were found to be in the range 9.5-11 Kcal/mol.