Yongkai Pan

Bio: Yongkai Pan is an academic researcher from ShanghaiTech University. The author has contributed to research in topics: Enantioselective synthesis & Kinetic resolution. The author has an hindex of 3, co-authored 4 publications receiving 20 citations. Previous affiliations of Yongkai Pan include Liaoning University of Petroleum and Chemical Technology.

Kinetic Resolution of Tertiary Benzyl Alcohols via Palladium/Chiral Norbornene Cooperative Catalysis

Abstract: Herein we report a highly enantioselective kinetic resolution of tertiary benzyl alcohols via palladium/chiral norbornene cooperative catalysis. With simple aryl iodides as the resolution reagent, a wide range of readily available racemic tertiary benzyl alcohols are applicable to this method. Both chiral tertiary benzyl alcohols and benzo[c]chromene products are obtained in good to excellent enantioselectivities (selectivity factor up to 544). The appealing synthetic utility of the obtained enantioenriched tertiary alcohols is demonstrated by the facile preparation of several valuable chiral heterocycles. Preliminary mechanism studies include DFT calculations to explain the origin of enantiodiscrimination and control experiments to uncover the formation of a transient axial chirality during the kinetic resolution step.

H-bond donor-directed switching of diastereoselectivity in the Michael addition of α-azido ketones to nitroolefins

Abstract: The development of catalyst-controlled stereodivergent asymmetric catalysis is important for providing facile access to all stereoisomers of chiral products with multiple stereocenters from the same starting materials. Despite progress, new design strategies for diastereodivergent asymmetric catalysis are still highly desirable. Here we report the potency of H-bond donors as the governing factor to tune diastereoselectivity in a highly diastereoselective switchable enantioselective Michael addition of α-azido ketones to nitroolefins. While a newly developed bifunctional tertiary amine, phosphoramide, preferentially afforded syn-adducts, an analogous squaramide catalyst selectively gave anti-adducts. The resulting multifunctional tertiary azides can be converted to spiro-pyrrolidines with four continuous stereocenters in a one-pot operation. Mechanistic studies cast light on the control of diastereoselectivity by H-bond donors. While the squaramide-catalyzed reaction proceeded with a transition state with both squaramide N–H bonds binding to an enolate intermediate, an unprecedented model was proposed for the phosphoramide-mediated reaction wherein an amide N–H bond and an alkylammonium ion formed in situ interact with nitroolefins, with the enolate stabilized by nonclassical C–H⋯O hydrogen-bonding interactions.