Kinetic Resolution of Oxaziridines via Chiral Bifunctional Guanidine-Catalyzed Enantioselective α-Hydroxylation of β-Keto Esters
作者:Xiaobin Lin、Sai Ruan、Qian Yao、Chengkai Yin、Lili Lin、Xiaoming Feng、Xiaohua Liu
DOI:10.1021/acs.orglett.6b01614
日期:2016.8.5
efficient kinetic resolution of racemic oxaziridines has been realized via catalytic asymmetric α-hydroxylation of available β-ketoesters. In the presence of a chiral bifunctional guanidine catalyst, a variety of optically active oxaziridines and chiral α-hydroxy β-ketoesters were generated with excellent results (ee’s of up to 99% and 97% and yields of up to 44% and 54%, respectively).
<scp>Monofluoromethyl‐Substituted</scp>
Sulfonium Ylides: Preparation,
<scp>Structure‐Reactivity</scp>
Study and Substrate Scope
<sup>†</sup>
作者:Xin Hong、Yafei Liu、Long Lu、Qilong Shen
DOI:10.1002/cjoc.202000206
日期:2020.11
Structure‐reactivity study of a family of electrophilic monofluoromethylating reagents based on sulfonium ylide skeleton with different steric hindrance and electron‐withdrawing properties was described. These studies led us to discover two highly reactive reagents 3 with a cyclic malonate backbone and 6 with an electron‐poor 1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione backbone. The high reactivity of reagent
Using visible light as a driving force and molecular oxygen as a green oxidant, we developed bis(oxazoline)–Ni(acac)2 catalyzed asymmetric α-hydroxylation of β-keto esters under low photosensitizer loading, and the protocol enabled an efficient transformation to provide the desired chiral α-hydroxy-β-keto esters in high yields (up to 99%) and enantioselectivities (up to 99% ee) at room temperature
Access to Both Enantiomers of α-Chloro-β-keto Esters with a Single Chiral Ligand: Highly Efficient Enantioselective Chlorination of Cyclic β-Keto Esters Catalyzed by Chiral Copper(II) and Zinc(II) Complexes of a Spiro-2,2′-bischroman-Based Bisoxazoline Li
bisoxazoline ligands (SPANbox) were found to be highly efficient in copper(II)‐ and zinc(II)‐catalyzed asymmetric chlorinations of cyclic β‐ketoesters with N‐chlorosuccinimide (NCS) as the chlorination reagent, to give the corresponding α‐chloro‐β‐ketoesters in excellent yields in 5–30 min with ee values up to 97%. The copper(II) triflate and zinc(II) triflate complexes of a single SPANbox ligand demonstrated
Although NHOs have been emerging as a new type of organocatalyst and ligand for metal complexes in organic synthesis, chiral NHO-mediated highly enantioselective organic transformations were still elusive. Herein, we developed a new type of chiral amine-derived C2-symmetric NHOs and employed them as efficient chiralbifunctionalorganocatalysts for asymmetric α-functionalization of β-ketoesters. With as