NEW [4-CYCLOADDITIONS TO TRIFLUORINATED DIENES(1])

Bis(trifluoromethyl)-4-methyl-2,5-dihydrothiophene (5), s(trifluoromet hyl)-4-methyl-2,5-dihydroselenophene (6), -trifluoromethyl-2,4-dimethy l-2,5-dihydrothiophene (7) and 2-trifluoromethyl-2,4-dimethyl-2,5-dihy dro (8) were prepared from ifluoro-4-trifluoromethyl-2-methyl-penta-1, 3-diene and 5,5,5-trifluoro-2,4-dimethyl-penta-1,3-diene by reaction w ith elemental sulphur or selenium. 5,5,5-Trifluoro-4-trifluoromethyl-p ent-3-en-2 and 5,5,5 trifluoro-4-methvl-pent-3-en-2-one were treated w ith bromine and HBr. The 1,4-dibrominated products isolated did not un dergo a metathesis reaction with K2S. (C) 1997 Elsevier Science S.A.