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

J Org Chem. 2021 Jan 15;86(2):1712-1720. doi: 10.1021/acs.joc.0c02524. Epub 2020 Dec 30.

Abstract

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.