Lei Yan, Hui-Qing Yang, Wan-Lei Yu, Xu-Gang Zhang, and Peng-Fei Xu*
https://doi.org/10.1021/jacs.5c03154
ABSTRACT:
Radical asymmetric reactions represent a crucial strategy in asymmetric synthesis, which is characterized by their high reaction efficiency and unique reactivity profiles. Despite significant progress in radical-based asymmetric transformations, the formation of C-N bonds using nonredox metal complexes via the inner-sphere stereocontrol mechanism remains a formidable challenge in the development of novel asymmetric catalytic strategies. This study introduces an innovative and highly efficient asymmetric photochemical bifunctional catalysis that utilizes a combination of magnesium salts and chiral PyBOX-type (pyridinebisoxazoline) C2-symmetric ligands under visible light irradiation. This approach enables the selective α-amidation of β-keto esters via an N-centered radical mechanism, facilitating the synthesis of substituted β-keto amino acid derivatives with a fully substituted stereocenter. The reaction proceeds in good yields (up to 79%) and excellent enantioselectivity (up to 94%). The catalysis proceeds through the in situ formation of prochiral quaternary charge-transfer complexes, which promote the Lewis acid-supported generation of radicals, thereby mediating the subsequent enantioconvergent radical-radical cross-coupling. Notably, the β-keto ester serves a trifunctional role as a sensitizer, reductant, and radical precursor, while the N-protected iminopyridinium ylide functions as both the oxidant and N-centered radical precursor. Experimental and computational mechanistic studies corroborate the enantioconvergent radical-radical cross-coupling process.
Yu Zhang, Hong Lu,* Jie Chang, Peng-Fei Xu, Hang Li, Yuan Jin, and Hao Wei*
https://doi.org/10.1002/anie.202500921
Bioisosteric replacement is an important strategy in drug discovery and is commonly practiced in medicinal chemistry; however, the incorporation of bioisosteres typically requires laborious multistep de novo synthesis. The direct conversion of a functional group into its corresponding bioisostere is of particular significance in evaluating structure-property relationships. Herein, we report a functional-group-exchange strategy that enables the direct conversion of aromatic lactones, a prevalent motif in bioactive molecules, into their corresponding cyclic hemiboronic acid bioisosteres. Scope evaluation and product derivatization experiments demonstrate the synthetic value and broad functionalgroup compatibility of this strategy, while the application of this methodology to the rapid remodeling of chromenone cores in bioactive molecules highlights its utility.
Jun-Bing Lin†, Dong-Sheng Ji† & Peng-Fei Xu*
https://doi.org/10.1007/s11426-023-1968-5
Organocatalytic cascade reactions represent a powerful strategy for the rapid construction of complex chiral molecules with multiple stereocenters from simple substrates under mild conditions. The intriguing structural feature and diverse reactivity of catalytically generated dienolate species render them competent and versatile intermediates for the development of practical and valuable cascade reactions. Over the past years, a plethora of innovative and pioneering noncovalent ammonium dienolatemediated cascade reactions have been designed and implemented under the catalysis of chiral organocatalysts, making dienolate activation a general, robust, and complementary method for the functionalization of unsaturated carbonyl compounds and related substances. This review illustrates the recent advances in organocatalytic noncovalent ammonium dienolate-mediated cascade reactions (mainly from 2010 to 2023), including the cascade transformations of ammonium dienolates directly generated from unsaturated ketone/aldehyde, ester/lactone/azlactone, amide/lactam/pyrazolone/oxindole, and alkylidene nitrile compounds. The contents are arranged based on the reaction types of the ammonium dienolates, with an emphasis on cascade 2,5-, 3,5-, and 4,5- difunctionalizations of these intermediates. Furthermore, other cascade reactions involving the 1,3-, 2,3-, and even more complex 3,4,5-reactivities of ammonium dienolates were also discussed. The reaction pathway, reaction stereoinduction, and synthetic applications of the ammonium dienolate-mediated cascade reactions were highlighted throughout the article. As a stimulating and ever-growing research area, the organocatalytic noncovalent ammonium dienolate-mediated cascade reactions are expected to continue demonstrating their magic power for constructing chiral targets in the future and further expanding the boundaries of asymmetric catalysis.
Hao-Wen Jiang, Wan-Lei Yu, Dong Wang, and Peng-Fei Xu*
https://doi.org/10.1021/acscatal.4c00401
Catalytic dehydrogenative borylation of alkenes is arguably the most straightforward approach for synthesizing alkenyl boronates, as it eliminates the need for alkene or boranes prefunctionalizion. While transition-metal catalysis has conventionally been employed for this transformation, competitive side reactions including hydroborylation, overborylation, and regioisomer formation always exist. In this study, we present a radical approach for catalytic dehydrogenative borylation, which involves the synergistic merger of photoredox/HAT/cobalt catalysis, thereby circumventing the necessity for noble metals, sacrificial hydrogen acceptors, and high temperatures. This method employs stable and cost-effective amine borane reagents as feedstocks, resulting in the sole byproduct of H2. This dehydrogenative borylation methodology facilitates the conversion of a diverse array of functionalized alkenes into valuable organoboron reagents. Furthermore, the late-stage borylation of complex molecules demonstrates high levels of site selectivity.
Hong Lu, Yu Zhang, Xiu-Hong Wang, Ran Zhang, Peng-Fei Xu & Hao Wei
https://doi.org/10.1038/s41467-024-48265-6
Developing skeletal editing tools is not a trivial task, and realizing the corresponding single-atom transmutation in a ring system without altering the ring size is even more challenging. Here, we introduce a skeletal editing strategy that enables polycyclic arenols, a highly prevalent motif in bioactive molecules, to be readily converted into N-heteroarenes through carbon–nitrogen transmutation. The reaction features selective nitrogen insertion into the C–C bond of the arenol frameworks by azidative dearomatization and aryl migration, followed by ring-opening, and ring-closing (ANRORC) to achieve carbonto-nitrogen transmutation in the aromatic framework of the arenol. Using widely available arenols as N-heteroarene precursors, this alternative approach allows the streamlined assembly of complex polycyclic heteroaromatics with broad functional group tolerance. Finally, pertinent transformations of the products, including synthesis complex biheteroarene skeletons, were conducted and exhibited significant potential in materials chemistry.
Guo-Qiang Xu*, Wei David Wang*, and Peng-Fei Xu*
https://doi.org/10.1021/jacs.3c06169
Owing to its diverse activation processes including single-electron transfer (SET) and hydrogen-atom transfer (HAT), visible-light photocatalysis has emerged as a sustainable and efficient platform for organic synthesis. These processes provide a powerful avenue for the direct functionalization of C(sp3)–H bonds under mild conditions. Over the past decade, there have been remarkable advances in the enantioselective functionalization of the C(sp3)–H bond via photocatalysis combined with conventional asymmetric catalysis. Herein, we summarize the advances in asymmetric C(sp3)–H functionalization involving visible-light photocatalysis and discuss two main pathways in this emerging field: (a) SET-driven carbocation intermediates are followed by stereospecific nucleophile attacks; and (b) photodriven alkyl radical intermediates are further enantioselectively captured by (i) chiral π-SOMOphile reagents, (ii) stereoselective transition-metal complexes, and (iii) another distinct stereoscopic radical species. We aim to summarize key advances in reaction design, catalyst development, and mechanistic understanding, to provide new insights into this rapidly evolving area of research.
Jia-Lu Zhang,†, Wen-Bo He,†, Xiu-Qin Hu, Peng-Fei Xu*
https://doi.org/10.1007/s11426-023-1819-8
http://:https://doi.org/10.1039/D3GC02955G
Using a formate salt as a promising hydrogen carrier and one-carbon (C1) source, we have developed a novel and practical method for the preparation of α-amino acid derivatives under mild conditions. In this approach, the photoexcited naphthalene thiolate acts simultaneously as a photoexcited single-electron reductant and a hydrogen atom transfer (HAT) catalyst, enabling efficient metal-free radical–radical cross-coupling of formate with ketimines and aldimines.
Sheng-Qiang Guo, Hui-Qing Yang, Yu-Zhen Jiang, Ai-Lian Wang, Guo-Qiang Xu, Yong-Chun Luo, Zhao-Xu Chen, Haixue Zheng and Peng-Fei Xu
https://doi.org/10.1039/D2GC00224H
Multicomponent diastereoselective synthesis is still very difficult to be achieved in photoredox catalysis. Here we report a green and reliable strategy for the diastereoselective synthesis of β-amido sulfones through the organophotoredox catalytic fourcomponent radical-polar crossover cascade reactions. This transformation features excellent atom-, step-, redox economy and diastereoselectivity. Moreover, DFT calculation studies are performed to provide some insights into the orign of diastereoselectivity.
Solvent Directed Chemically Divergent Synthesis Of β-lactams And α-amino Acid Derivatives With Chiral Isothiourea
Dong-Sheng Ji, Hui Liang, Kai-Xuan Yang, Zhi-Tao Feng, Yong-Chun Luo, Guo-Qiang Xu, Yucheng Gu, Peng-Fei Xu
https://doi.org/10.1039/d1sc06127e
Abstract
A protocol for the chemically divergent synthesis of β-lactams and α-amino acid derivatives with isothiourea (ITU) catalysis by switching solvents was developed. The stereospecific Mannich reaction occurring between imine and C(1)-ammonium enolate generated zwitterionic intermediates, which underwent intramolecular lactamization and afforded β-lactam derivatives when DCM and CH3CN were used as solvents. However, when EtOH was used as the solvent, the intermediates underwent an intermolecular esterification reaction, and α-amino acid derivatives were produced. Detailed mechanistic experiments were conducted to prove that these two kinds of products came from the same intermediates. Furthermore, chemically diversified transformations of β-lactam and α-amino acid derivatives were achieved.
