Organocatalyzed Asymmetric Michael Addition of 4‐Monosubstituted‐pyrazol‐5‐ones to Enones: Construction of Vicinal Quaternary and Tertiary Stereocenters
Pyrazolone moiety bearing an all-carbon quaternary stereogenic center is frequent in biologically active products and pharmaceuticals. The catalytic route for the construction of a quaternary carbon center possesses challenges. In this report, catalytic asymmetric Michael addition of 4-monosubstituted-pyrazol-5-ones to simple enones catalysed by primary amine-Brønsted acid composite has been developed. An array of pyrazolone derivatives bearing vicinal all carbon quaternary and tertiary stereocenters, were obtained in moderate to good diastereoselectivities (up to 92:8 dr) and good to excellent enantiomeric excess (up to 99% ee). In addition, antipode for enantiomers of the pyrazolone derivatives were also be realized in good to high stereoselectivities (up to 92:8 dr and up to 98% ee).
