Highly enantio- and diastereoselective construction of spirocyclic oxindoles via a palladium-catalyzed decarboxylative asymmetric [4 + 2] annulation strategy
A palladium-catalyzed decarboxylative asymmetric [4 + 2] annulation of methyleneindolinones with a zwitterionic oxo-1,4-dipole intermediate was successfully developed to access spirocyclic oxindoles bearing two vicinal stereocenters in good yields with high diastereoselectivities and enantioselectivities. This strategy features a broad substrate scope (28 examples), allowing for efficient scale-up
A highly enantioselective [4+2] annulation with respect to allenoates and 3-olefinic oxindoles catalyzed by Lewis base was reported, which proved to be an efficient way to synthesize chiral dihydropyran-fused indoles. The cycloaddition products were generally obtained in high yields (up to 98%) with very good enantioselectivities (up to 94% enantiomeric excess).