Development of palladium-catalyzed transformations using propargylic compounds.

It is known that propargylic compounds having an ester and a halide at the propargylic positions react with palladium complexes leading to π-propargylpalladium and allenylpalladium complexes, which cause various transformations in the presence of the reactants. The aim of the present study was to develop novel palladium-catalyzed transformations using propargylic compounds. As diastereoselective reactions of propargylic compounds with bis-nucleophiles, we have developed palladium-catalyzed reactions of propargylic carbonates with 2-substituted cyclohexane-1,3-diones, 2-(2-hydroxyphenyl)acetates and 2-oxocyclohex-3-enecarboxylates. These processes produce highly substituted cyclic compounds in a highly stereoselective manner. Through our studies on the construction of substituted 2,3-allenols by the reactions of propargylic oxiranes, it has been made clear that palladium-catalyzed coupling reactions occur in the presence of arylboronic acids and terminal alkynes. The processes can be carried out in mild conditions to yield substituted 4-aryl-2,3-allenols in a diastereoselective manner. In our attempt to develop CO2-recycling reactions, we developed a methodology for the synthesis of cyclic carbonates by palladium-catalyzed reactions of propargylic carbonates with phenols. Our findings suggested that the process proceeds through a pathway involving decarboxylation-followed fixation of the liberated CO2. Diastereoselective, enantioselective, and enantiospecific construction of cyclic carbonates have been achieved by the application of this methodology.