Diastereoselective and Enantioselective Synthesis of Barbiturate-Fused Spirotetrahydroquinolines via Chiral Palladium(0)/Ligand Complex Catalyzed [4 + 2] Cycloaddition of Vinyl Benzoxazinanones with Barbiturate-Based Olefins

Under
the catalysis of chiral palladium(0)/ligand complex, the
[4 + 2] cycloaddition between vinyl benzoxazinanones and barbiturate-based
olefins proceeded readily and provided barbiturate-fused spirotetrahydroquinolines
in up to 96% chemical yield with up to >99:1 dr and 97% ee. The
absolute
configuration of barbiturate-fused spirotetrahydroquinolines was clearly
identified by X-ray single crystal structure analysis. The reaction
mechanism was proposed to shed light on the enantioselective formation
of barbiturate-fused spirotetrahydroquinolines.