Asymmetric organocatalytic conjugated addition of pyrazolin-5-ones to ortho-quinomethanes: construction of vicinal tertiary and all-carbon quaternary stereocenters

A chiral amine squaramide catalyzed the conjugated addition of pyrazolin-5-ones to in situ generated ortho-quinomethanes (o-QMs) was developed to construct 4-tetrasubstituted pyrazolin-5-ones featuring adjacent quaternary and tertiary stereocenters in oil-water phases. High yields, excellent stereoselectivities, mild conditions and accessible scale-up demonstrated the fascination of this reaction protocol.