Synthesis and chemistry of fluorinated polyenes cis-trans isomerization of the 1,2-difluoroolefinic unit in conjugated dienes

Fluorinated dienes and trienes have been prepared in good yields by the Pd(PPh{dollar}sb3)sb4{dollar} or CuI catalyzed cross-coupling reaction of a 1,2-difluorovinyl iodide and the trifluorovinylzinc reagent under mild conditions.{dollar}sp*{dollar} enspace; {dollar}alpha,beta,beta{dollar}-Trifluorostyrenes have been converted to the corresponding trans-{dollar}alpha{dollar}-iodo-{dollar}alpha,beta{dollar}-difluorostyrenes by reaction with Bu{dollar}sb3{dollar}P and {dollar}rm BFsb3{lcub}cdot{rcub}Etsb2O{dollar} in DMF, followed by quenching with KF and iodine. trans-{dollar}alpha{dollar}-Iodo-{dollar}alpha,beta{dollar}-difluorostyrenes were also prepared by the reaction of KF and iodine with trans-{dollar}alpha{dollar}-triethylsilyl-{dollar}alpha,beta{dollar}-difluorostyrenes. The two methodologies complement each other and provided access to the whole spectrum of trans-{dollar}alpha{dollar}-iodo-{dollar}alpha,beta{dollar}-difluorostyrenes.; trans,trans-HCF=CFCF=CFSiEt{dollar}sb3{dollar}, 1, projected as a trans,trans-tetrafluorobutadiene synthon, has been successfully prepared from the LiAlH{dollar}sb4{dollar} reduction or hydrolysis of the phosphonium salt of trans-CF{dollar}sb2{dollar}=CFCF=CFSiEt{dollar}sb3{dollar}. trans,trans-HCF=CFCF=CFI and trans,trans-ICF=CFCF=CFSiEt{dollar}sb3{dollar} have been prepared from 1.; A novel trans-to-cis iodine-induced isomerization of the 1-hydro-1,2-difluoroolefinic unit in conjugated dienes has been discovered for the first time. It allows the stereospecific preparation of several tetrafluorobutadiene synthons containing the cis-difluoro configuration, including cis,trans-HCF=CFCF=CFSiEt{dollar}sb3{dollar}, cis,trans-difluoroconfiguration, including cis,trans-HCF=CFCF=CFSiEt{dollar}sb3{dollar}, cis,trans-ICF=CFCF=CFSiEt{dollar}sb3{dollar}, and cis,trans-Bu{dollar}sb3{dollar}SnCF=CFCF=CFSiEt{dollar}sb3{dollar}, and opens an entire new area of organofluorine chemistry with cis-difluoro configurations.{dollar}sp*{dollar}; A series of trans- and cis-2-substituted-1,2-difluoroethenylstannanes are readily prepared in good yield by the reaction of the corresponding fluorinated alkenyl silanes with Bu{dollar}sb3{dollar}SnCl and KF in DMF under mild conditions. To our knowledge this work is the first report of the stereospecific conversion of a vinyl silane to the corresponding vinylstannane. The discovery initiated several other related projects in our research group on the chemistry of fluorinated vinylstannanes and their utilization in the synthesis of other fluorinated olefins which were not easily prepared by earlier methodology.{dollar}sp*{dollar} enspace{dollar}{dollar}rm RCF=CFSiEtsb3quad {lcub}{lcub}KF, Busb3SnClatoplongrightarrow{rcub}atop{lcub}RT, DMFatopquad{rcub}{rcub}quad RCF=CFSnBusb3{dollar}{dollar} ftn{dollar}sp*{dollar}Please refer to the dissertation for diagrams.