Asymmetric palladium-catalyzed decarboxylative [3+2] cycloaddition: straightforward construction of chiral spiro-heterocyclic scaffolds

A novel asymmetric Pd-catalyzed decarboxylative [3 + 2] cycloaddition of vinylethylene carbonates and alpha,beta-unsaturated pyrazolones has been developed to afford highly functionalized tetrahydrofuran-fused spiro-heterocyclic skeletons with excellent stereoselectivity. A diverse range of enantioenriched spiro-tetrahydrofuran-pyrazolones, possessing three contiguous stereogenic centers including one all-carbon quaternary, were obtained in high yields and excellent enantioselectivities (up to 90% yield and 98% ee). In addition, the practical application of this protocol was also demonstrated by gram-scale synthesis and further transformations into various compounds. Preliminary mechanistic experiments indicated that the allylic 1, 3-strain was crucial to the stereoselective control. We developed an asymmetric Pd-catalyzed [3 + 2] cycloaddition of alpha,beta-unsaturated pyrazolones with vinylethylene carbonates. An array of spiro-tetrahydrofuran-pyrazolones were obtained in high yields with excellent enantioselectivities.