Isomerization Reactions Induced By Gold Or Palladium Catalyzed Alkene Or Alkyne Activation

Transition metal catalyzed C-C multiple bonds activation-functionalization reaction is an important methodology to construct C-C bond and C-heteroatom bond. The key intermediate of this reaction-alkyl metal or vinyl metal species, is highly reactive which could be utilized for further transformations, such as further functionalization and isomerization reactions. This concept provided a general strategy for the rapid and efficient access to a variety of complex molecules.Gold catalyst shows ubiquitous affinity to active C-C ? bond with superior reactivity, selectivity and functional group tolerance. This area has experienced a breakthrough over the past decade. Abundant methodologies were reported demonstrating the powerful ability of gold catalysis in alkyne activation reactions to synthesize all kinds of complex molecules. Among all of these transformations, asymmetric cationic Gold(I) catalysis is the edge of this field.In the first project, the author describes the results of gold(I) catalyzed asymmetric alkoxylation-Claisen rearrangement of alkyne substrates. Based on the previous report, the author developed an chiral ligand controlled, Au(I) catalyzed enantioselective alkoxylation/Claisen rearrangement of symmetric 1,4-diene containing alkyne substrate. This reaction provides a convenient approach to optical pure and highly functionalized cycloheptenes or their fused ring analogues which are frequently observed in abundant natural products and pharmaceuticals. Mechanistic study reveals that the desymmetrization of the 1,4-diene moiety is the key step for the success of the enantiomer discrimination. A concerted process is dominant during the reaction along with a small amount of stepwise cationic process, which caused the decline of enantioselectivity.In the second project, the author and coworker developed an Au(?) catalyzed asymmetric dearomative Rautenstrauch rearrangement based on indole containing propargylic acetal substrates. It is the first example of highly enantioselective Rautenstrauch rearrangement controlled by chiral ligand. Optical pure cyclopenta[b]indole products were obtained rapidly which represented common structure skeletons of a series of bio-active molecules. Mechanistic study revealed that the slightly changing from propargylic ester to propargylic acetal as the substrate significantly enhance the chirality inducement during the reaction. This benefit results from the facile leaving ability of acetal group. It facilitates the formation of achiral intermediate and thus reduces the activation energy of kinetic dynamic resolution process.Palladium catalyzed olefin activation is a classic topic which is still under fast development recently. Among all those methodologies, high valent palladium catalysis (Pd?/Pd? cycle or Pd?/Pd? cycle) has become the frontier of this field. Compared to the low valent palladium complex, the high valent palladium ones exhibit a number of superior or complementary reactivities, such as the features of enhanced reductive elimination, inhibited ?-hydride elimination, insensitivity to air and so on. Olefin difunctionalization and C-H functionalization have appeared to be the two major areas wherein these features are well applied. More and more examples are reported recently which showed the powerful ability of high valent palladium catalysis in challenging C-X bond constructions, e.g., C-halogen(heavy), C-F and C-CF3 bond.The third project in this paper describes an unusual high valent palladium mediated isomeric olefin difunctionalization reaction. The author discovered a high valent palladium mediated olefin oxy-palladation, Wagner-Meerwein type rearrangement and fluorination cascade reaction to access fluorinated oxazolidine-2,4-dione and oxazolidine-2-one moieties. Further study revealed that the reaction was initiated by an anti-oxy-palladation step followed by oxidation generating the key alkyl PdIV intermediate. Different from the previous report, this intermediate didn't undergo direct reductive elimination or C-H activation reaction as the major pathway. Instead, a cation induced 1,2-shift occurred to generate the more stable a-oxygen carbon cation. This species further reacted with fluorine anion to provide the observed product. The deuterium labelling experiment showed that both concerted and stepwise migration-fluorination processes are involved during the reaction. The former process is predominant and the latter one causes the diminishment of diastereoselectivity of the product. This reaction offers a completely different strategy to develop new transformations mediated/catalyzed by high valent palladium intermediates.