Diels–Alder reactions of polyfluorocyclohexa-1,3-dienes. Part I. Addition of alkynes to perfluorocyclohexa-1,3-diene. A route to ortho-disubstituted tetrafluorobenzenes

Abstract

Perfluorocyclohexa-1,3-diene reacts with alkynes (I) by 1,4-addition to give, exclusively and in good yield,2,3-disubstituted-1,4,5,6,7,7,8,8-octafluorobicyclo[2,2,2]octa-2,5-dienes (II)(X = Y = CF₃, Me, Ch₂Cl, CO₂Et; X = H, Y = CF₃, Me, Ch₂Cl, Ph; X = CF₃, Y = Me) which eliminate tetrafluoroethylene on pyrolysis to give ortho-disubstituted tetrafluorobenzenes, or their further pyrolysis products (III)(X = Y = CF₃, Me, H; X = H, Y = CF₃, Me, CH₂Cl, CO₂H, –CCH, CHCH·C₆HF₄, Ph; X = CF₃, Y = Me).