Palladium Or Rhodium Catalysed Alkene Functionalization Reaction

Pyrone structural subunits are widely observed in many natural products and pharmaceutical molecules.Forthermore,pyrones are also useful building blocks for the synthesis various other functional compounds.Consequently,the construction of this class of compounds has attracted much attention to organic chemists.As we all known,traditional approaches have been developed to synthesize those compounds.However,limited substrate scope and/or harsh reaction conditions still restrict the wide application of these methods.Therefore,the development of simple and effective methods to prepare those functional pyrones is still challenging.Fluorine,’small atom with a big ego’,due to its intrinsic properties such as small size and high electronegativity in comparison with other halogen atoms,has played a key role in all fields of science.More specifically,the introduction of fluorine atom into a molecule will bring about substantial improvement in its bioactivity and unique chemical and physical properties.Thus it enables the widespread use of this strategy in the field of medicinal chemistry,materials and drugs etc.This dissertation include two chapters:Chapter 1:Palladium catalyzed difunctionlization of internal alkynes via highly regioselective 6-endo cyclation and alkenylation of enynoates to synthesize multisubstituted pyrones.We have developed a Pd(Ⅱ)-catalyzed highly regioselective 6-endo cyclization alkenylation tandem reactions.Various multisubstituted pyrones were obtained in good yields under mild reaction conditions in a one-pot manner,which provided a chance for the synthesis of natural derivatives containing pyrone fragment.Chapter 2:Rhodium or Palladium catalyzed cross-coupling reaction of gem-difluoroalkenes to synthesize fluorine-containing compounds.In this chapter,gem-difluoroalkenes were used as the starting materils to succesufully syhthesized cis-alkenyl fluorides and homoallyltrifluoromethane derivatives in the presence of rhodium or palladium catalyst.Part 1:We developed a highly effective Rh(III)-catalysed a-fluoroalkenylation of(hetero)arenes through C-H activation and C-F cleavage.This reaction proceeds smoothly under mild reaction conditions to deliver a diverse synthetically useful and pharmaceutically relevant cis-alkenyl fluorides in good yields and with excellent stereoselectiveties.Furthermore,no base and oxidant were needed in this reaction and the scopes of the protocols were broad.This method may provide a simple way in the synthesis of functionalized fluoroalkene derivatives.Last but not the least,the involvement of activation of the C-F bond through hydrogen-bond formation is crucial for the success of this transformation.The sole byproduct is hydrofluoric acid,which shows a good atom-economy.Part 2:We developed palladium-catalyzed three-components reactions to synthesize various homoallyltrifluoromethane derivatives in an effective way.This threecomponent transformation is characterized by its well-organized reaction sequence,thus obviating the potential side pathways.