Synthesis and dienophilic reactivity of 1,2-difluorovinylphenylsulfone

1,2-Difluorovinylphenylsulfone 5 was conveniently prepared in three steps from chlorotrifluoroethylene. Both E and Z isomers of 5 gave excellent yields of [4+2] cycloadducts with cyclopentadiene. The E isomer reacted with high kinetic exo selectivity. 1,2-Difluorovinylphenylsulfone 5 did not give cycloadducts with highly polar and reactive dienes. Only complex mixtures were obtained. This was assigned to competitive pathways resulting from addition-elimination sequences. Products resulting from such an addition-elimination sequence were obtained from representative nucleophilic reagents. (C) 1997 Elsevier Science Ltd