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    Home > Zhang Wanbin, Professor of Shanghai Jiaotong University: the construction of stereochemistry complex pyrazoline compounds by asymmetric aza Wacker type cyclization of tetrasubstituted alkenes

    Zhang Wanbin, Professor of Shanghai Jiaotong University: the construction of stereochemistry complex pyrazoline compounds by asymmetric aza Wacker type cyclization of tetrasubstituted alkenes

    • Last Update: 2018-06-12
    • Source: Internet
    • Author: User
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    The author: Dr Kou Xuezhen's chiral nitrogen-containing heterocyclic compounds exist in many natural products and drugs Transition metal catalyzed intramolecular amination of olefins is a very effective method for the construction of nitrogen-containing heterocyclic compounds Asymmetric aza Wacker type cyclization is a very important method to construct chiral nitrogen heterocycles Professor Zhang Wanbin's research group of Shanghai Jiaotong University has done a series of pioneering work in this field At first, the team developed biphenyltetraxazoline ligands and 5,5 '- bridged biphenyldixazoline ligands, which obtained good experimental results in asymmetric oxo Wacker type reaction (t etrahedron lett 2007, 48, 4083; J org Chem 2007, 72, 9208) Then, on the basis of this work, they studied the more challenging asymmetric aza Wacker type cyclization In 2010, Jiang Feng, a doctoral student of the research group, applied quinoline oxazoline ligands to asymmetric aza Wacker type cyclization (Tetrahedron lett 2010, 51, 5124) Using IPR quinox / Pd (OAC) 2 / toluene / O2 catalyst system, the EE value reported in the previous literature can be increased from 10% to 74% In 2012, Yang Guoqiang, a doctoral student of the research group, realized the first asymmetric aza Wacker type cyclization of n-methoxyamide substrate by using t bu-pyrex / Pd (TFA) 2 / MeCN / O 2 catalyst system, and successfully constructed the isoindolone structure with chiral α - tertiary amine (angelw Chem., int ed 2012, 51, 9141) Recently, the group has made new progress in the study of asymmetric aza Wacker type cyclization: a case of intramolecular asymmetric aza Wacker type cyclization using TBU pyrox / Pd (OAC) 2 / acetone / O 2 catalyst system for tetrasubstituted monoolefin substrate was successfully developed for construction Pyrazoline compounds (J am Chem SOC., DOI: 10.1021 / JACS 8b02865) with one tetrasubstituted carbon chiral center and two consecutive chiral centers By optimizing the experimental conditions such as catalyst, ligand, solvent and temperature, the author found that TBU Pyrex / Pd (OAC) 2 / acetone / O 2 catalyst system can obtain pyrazoline products with four substituted carbon chiral centers with high enantioselectivity The results show that the catalytic system is suitable for hydrazone bonded substrates with different substituents such as aryl, heterocycle, alkyl and other substituents, as well as four substituted alkenes with different substituents It is worth noting that the substrate containing styryl does not react with n-ts hydrazine in this catalytic system (Fig 1) Fig 1 asymmetric aza Wacker type reaction to construct pyrazoline with single chiral center (source: J am Chem SOC.) is worth noting that when two methyl groups at the position of terminal alkene are replaced by two ethyl groups, the product is mainly the product with continuous two handed center that the alkene migrates to the end By changing different substituent groups, it is found that when the two lateral substituent groups R 2 and R 3 of alkene are more linear alkyl than methyl, β - hydrogen elimination reaction will take place preferentially on the alkene substituent group (R 3) in the cis position with the nucleophile in the molecule At the same time, the author observed another interesting phenomenon in the asymmetric aza Wacker type reaction: when one of the two alkyl substituent groups R2 and R3 on the outermost side of alkene is methyl, the reaction will be more likely to occur on the methylene side larger than the methyl, rather than on the methyl side Therefore, a pair of diastereomers can be obtained by changing the CIS trans structure of olefins (Fig 2) Fig 2 in the mechanism study of asymmetric aza-Wacker-type reaction for the construction of pyrazoline with two consecutive chiral centers (source: J Am Chem Soc.), the author designed and synthesized the substrate with methyl and benzyl groups in the trans position The palladium metal catalyst can only be eliminated in a cis way when β - hydrogen is eliminated, so the substrate can be used to study the mechanism of amine palladization The experimental results show that the palladization mechanism of CIS amines is not changed when Hoac is added or Pd (TFA) 2 is used as catalyst (Fig 3) Fig 3 study on the mechanism of amine palladization (source: J am Chem SOC.) in order to further confirm the group selectivity in the construction of the second chiral center, the author designed and synthesized an isotope labeled substrate Under the standard conditions, all the products are the products of β - hydrogen elimination of methylene on R3 group and migration of olefin to the end This result further shows that when the R 2 and R 3 groups are linear alkyl groups larger than the methyl group, the β - hydrogen elimination reaction will take place preferentially on the R 3 group (Fig 4) Fig 4 production of the second chiral center (source: J am Chem SOC.) by isotope labeling experiment The research results were recently published in Journal of the American Chemical Society The first author of the paper is Kou Xuezhen, a doctoral student from Shanghai Jiaotong University, and the corresponding authors are Mr Yang Guoqiang and Prof Zhang Wanbin This work is supported by NSFC, Shanghai Science and Technology Commission and Shanghai Education Commission in scientific research funds Thesis information: Xuezhen Kou, qihangshao, Cheng ye, Guoqiang Yang *, and Wanbin Zhang *, asymmetrical aza Wacker type cyclization of N - TS hydrazine tethered tetrasubstituted olefins: synthesis of pyrazolines bearing one quality or two vital anchors, J am Chem SOC., 2018, Doi: 10.1021/jacs.8b02865 Review of previous reports by Professor Zhang Wanbin, research group of Shanghai Jiaotong University: Copper catalytic synergistic reaction of reduction and defluorination of β - trifluoromethylenone and oxidative coupling of Grignard reagent by Professor Zhang Wanbin, research group of Shanghai Jiaotong University: IR / Cu bimetal synergistic catalytic system for non natural α, Three dimensional divergent synthesis of α - disubstituted α - amino acids
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