Asymmetric Synthesis of Spiropyrazolones via Chiral Pd(0)/Ligand Complex-Catalyzed Formal [4+2] Cycloaddition of Vinyl Benzoxazinanones with Alkylidene Pyrazolones

In
the presence of the chiral Pd(0)/ligand complex, vinyl benzoxazinanones
underwent the [4+2] cycloaddition with alkylidene pyrazolones smoothly
and delivered spiropyrazolones in reasonable yields, diastereoselectivities,
and eneantioselectivities (up to >99% yield, >99:1 dr and 99%
ee).
The absolute configuration of the obtained spiropyrazolones was unambiguously
characterized with the use of X-ray single-crystal structure analysis.
Moreover, the reaction mechanism was assumed to interpret the formation
of the target compounds.