Stereoselective synthesis of substituted (E) and (Z)-difluoroethenyl derivatives

A series of perfluoro-1-iodo-1-alkenes were prepared via the coupling reaction of pregenerated perfluoroalkyl copper reagents and (E)-CFI=CFSiEt;The synthetic utility of 6 was demonstrated via reaction with the diethyl difluoromethylphosphonate cadmium reagent (11) in the presence of CuBr to yield the (E)-perfluoroallylic phosphonates (7). To afford the corresponding perfluorovinyl zinc reagents (8) 6 was treated with activated zinc metal. The vinyl zinc reagent, 8, underwent palladium(0) catalyzed coupling with an aryl iodide (1-iodo-4-nitrobenzene).*.;A novel synthesis of perfluorocyclobutenes was discovered via the reaction of excess perfluoroalkyl copper reagent with (E)-CFI=CFI. A preliminary mechanistic study led to a proposed pathway of cyclization.*.;The corresponding (Z)-difluoroethenyl systems were synthesized from (Z)-CFI=CFI. The synthetic pathways for two distinct systems were explored; the symmetrical (Z)-1,2-difluorostilbenes and the (Z)-3,4-difluoro-1,5-diyne-hexa-3-enes. The enediynes were generated from (Z)-CFI=CFI via palladium(II) catalyzed coupling with terminal alkynes.*.;The unsymmetrical enediynes could be synthesized via (Z)-CFI=CFSiEt...