MILD, ZINC-INDUCED DEFLUORINATION OF BUTATRIENES - STEREOSELECTIVE FORMATION OF DIVINYLACETYLENE DERIVATIVES

Defluorination of R(Ph)C=C=C(Ph)R [R = C2F5 (3b); R n-C3F7 (3c)] was a ccomplished: under remarkably mild conditions: Zn/rt/18 h. Reaction of pure (E)- or (Z)-3b with Zn gave in both instances 89-96% (E,E)-CF3CF =C(Ph)C=CC(Ph)=CFCF3 in greater than 95% isomeric purity. The latter p roduct was characterized by X-ray crystallography. Similarly, treatmen t of pure (E)or (Z)-3c with Zn gave 70-93% CF3CF2CF=C(Ph)C=CC(Ph)=CFCF 2CF3 in 95% isomeric purity, although the stereochemistry could not be determined. A single electron transfer (SET) mechanism is proposed fo r the defluorination reaction.