ABSTRACT Reaction of halogen electrophiles (Cl2, Br2, or ICl) with 1,1,2-trifluorobut-1-en-4-ol (6) and 3-buten-1-ol (7) give dihalo products 9 and cyclized 3-halofurans (11). Vinyl fluorines stabilize positive charge on the carbons of the three-membered halonium ions better than hydrogen. This is supported by the greater amount of rearranged furan products from the trifluoroalkene 6 than the hydrocarbon alkene 7. Halonium ions from 6 and 7 are rather symmetrical except for the ionic reaction of chlorine with 6 where the three fluorines stabilize the positive charge sufficiently such that open-ion intermediates 12 and 13 are indicated.
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