Pd-catalyzed sequential intramolecular annulation/intermolecular [3+2] cycloaddition of 5-allenyloxazolidine-2,4-diones with dipoles: synthesis of spiroheterocycles

Pd-catalyzed sequential intramolecular annulation/intermolecular [3+2] cycloaddition of 5-allenyloxazolidine-2,4-diones with dipoles was achieved. Under palladium catalysis, various 5-allenyloxazolidine-2,4-diones reacted with 1,3-dipoles such as nitrile N-oxides, azomethine imines or nitrilimines to give a series of functionalized spiroheterocycles in high yields. The scale-up reaction and further derivation of products were successful. A plausible mechanism was also proposed based on the control experiments. A new reaction pattern of 5-allenyloxazolidine-2,4-diones was achieved under palladium catalysis.