Bifunctional Squaramide‐Catalyzed One‐Pot Sequential Michael Addition/Dearomative Bromination: Convenient Access to Optically Active Brominated Pyrazol‐5(4H)‐ones with Adjacent Quaternary and Tertiary Stereocenters. Issue 22 (17th June 2013) - Wang, Huanxia
Abstract: The organocatalytic asymmetric, one‐pot, sequential Michael addition/dearomative bromination reaction of pyrazol‐5‐ones to nitro olefins and N ‐bromosuccinimide (NBS) has been developed. Under the catalysis of a chiral bifunctional squaramide, a wide variety of chiral brominated pyrazol‐5‐one derivatives with contiguous quaternary and tertiary stereocenters was obtained in high yields (up to >99 %) with good to excellent diastereoselectivities (62:38–99:1 dr ) and uniformly high levels of enantioselectivity (92 to >99 % ee ). This experimentally simple process facilitates access to various enantioenriched, multiply substituted pyrazolin‐5‐one derivatives, potential biologically active molecules, starting from readily available starting materials. Abstract : A one‐pot synthesis of optically active brominated pyrazol‐5‐one derivatives bearing contiguous quaternary and tertiary stereocenters has been developed. The asymmetric, sequential Michael addition/dearomative bromination reaction of pyrazol‐5‐ones and nitro olefins is catalyzed by a bifunctional squaramide.