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Catalytic Asymmetric Conjugate Addition of Pyrazolin-5-ones
Z. Wang, Z. Yang, D. Chen, X. Liu, L. Lin, X. Feng*
Sichuan University, Chengdu, P. R. of China
19 August 2011 (online)
This conjugate addition process is catalyzed by a combination of a Lewis acid and a chiral N,N′-dioxide ligand. The highly enantio-enriched product, which is a pyrazolone derivative, bears contiguous tertiary and quaternary stereocenters. Remarkably, changing the Lewis acid and the solvent results in a switch in enantioselectivity. These inverse effects between Sc and Y may also be observed in other asymmetric reactions.