Investigation On Palladium-Catalyzed Coupling Reactions Of Alkynes And Alkenes For The Synthesis Of N-and/or O-Containing-Heterocyclic Compounds

As an important tool to construct C-C/C-hetero atom bonds,transition metal-catalyzed coupling reaction has been one of the most active research fields in organic synthesis.Among those transition metals,palladium plays an important role due to its good selectivity,high catalytic efficiency,good functional group tolerance.Besides,there exist four easily interconvertible oxidation states of palladium complexes,Pd?0?,Pd?II?,Pd???and Pd?IV?,which can be tuned by varying the ligands,bases,oxidants and additives,leading to the diversification of the reaction models for more complex organic framworks.On the other hand,as important petrochemical raw materials,alkenes and alkynes are the base materials of national economics and sustainable development and have been applied to the fields of organinc synthesis,materials science,and pharmaceutical synthesis.How to achieve more efficient and green transformations of those raw materials forming high value-added industrial products has been a challenging goal.Based on the backgrounds above,this thesis focused on the investigation on the palladium-catalyzed cross coupling reactions between alkenes and alkynes.Several environmentally friendly and highly efficient/selective methods has been developed for the construction of N and/or O-containing heterocyclic compounds.The details are as follows:In Chapter two,we report a novel palladium-catalyzed cascade carboesterification of norbornene with alkynes for the synthesis of?-methylene?-lactone and tetrahydrofuran with O₂ as green oxidant and HOAc/Ac₂O as co-solvent.This method performed easy materials and mild reaction conditions with good substrate scope and functional tolerance.In this transformation,C?sp²?-C?sp²?/C-O/C?sp²?-Cl bonds could be formed in one step.In Chapter three,a palladium-catalyzed cascade annulation/allylation or alkylation of alkynyl oxime ethers with?-1-alkenyl halides for the synthesis of fully substituted isoxazoles has been developed.In this reaction,3 mol%of Pd?OAc?₂ was employed and oxidant/base were not needed.Besides,the reaction was efficient,and the assemble of 4-allyllated isoxazoles could finish in 5-40 min.In Chapter four,we report the synthesis of?-isoxazole carbonyl derivatives and their analogues by palladium-catalyzed cascade C?sp²?-O/C?sp²?-C?sp³?bond formation under mild conditions.Mechanistic studies reveled that oxypalladation,immigration of alkenes,?-H elimination and enol isomerization were involved in this transformation.In Chapter five,a novel N-heterocyclic carbene palladium-catalyzed cascade annulation/alkynylation of 2-alkynylanilines with terminal alkynes for the construction of 3-alkynylindols under air atmosphere has been developed.This protocol features mild conditions,broad substrate scope,as well as high atom-and step-economy.