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 (Rf)2Sx. Due to broadening of signals in 19F 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.