Diels–Alder reactions of polyfluorocyclohexa-1,3-dienes. Part II. Addition of nitriles to perfluorocyclohexa-1,3-diene. A route to 2-substituted tetrafluoropyridines

Abstract

Perfluorocyclohexa-1,3-diene reacts by 1,4-addition at high temperatures and pressures with nitriles RCN (I) which have highly electronegative substituents (R = CF₃, Br, C₆F₅ and [CF₂]₃CN). The 3-substituted octafluoro-2-azabicyclo[2,2,2]octa-2,5-dienes (II) so formed are generally unstable under the reaction conditions and either undergo retro-Diels–Alder addition or spontaneously eliminate tetrafluoroethylene to give the corresponding 2-substituted tetrafluoropyridines (III). Perfluoroglutaronitrile also gives, in low yield, perfluoro-1,3-bis-(2-pyridyl)propane by double addition and elimination.