Decarboxylation-promoted Pd-catalyzed asymmetric propargylic [3 + 2] annulation for the enantioselective construction of a quaternary stereocenter in 2,3-dihydrofurans

摘要

The enantioselective construction of a quaternary stereocenter in 2,3-dihydrofuran frameworks has been realized via the palladium-catalyzed asymmetric [3 + 2] cycloaddition of tertiary propargylic carbonates with p-ketoesters enabled by a chiral ferrocene/benzimidazole-based bidentate P,N-ligand. The reaction was significantly promoted by loss of CO_2 to irreversibly form jt-propargylpalladium or allenylpatladium intermediates. This protocol features a good tolerance of functional groups in both tertiary propargylic carbonates and p-ketoesters, thereby delivering a variety of highly functionalized chiral 2,3-dihydrofurans bearing a quaternary stereocenter at the 2-position and an exocyclic double bond at the 3-position in good chemical yields and high enantioselectivities (up to 98% ee).