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38 results on '"Zhong, Kangbao"'

33. σ-Bond Migration Assisted Decarboxylative Activation of Vinylene Carbonate in Rh-Catalyzed 4 + 2 Annulation: A Theoretical Study

Author

Shen, Boming, Liu, Song, Zhu, Lei, Zhong, Kangbao, Liu, Fenru, Chen, Haohua, Bai, Ruopeng, and Lan, Yu

Abstract

As a C2 synthon, vinylene carbonate has been used instead of acetylene in transition-metal catalyzed-coupling reactions. In this study, the mechanism of the vinylene carbonate activation mode for the Rh(III)-catalyzed 4 + 2 annulation of benzamide and vinylene carbonate reaction is proposed, and it was investigated by DFT with the M06 density functional. The computational results show that the proposed reaction pathway, which includes the insertion of vinylene carbonate into an Rh–C bond, decarboxylation of the seven-membered rhodacycle intermediate, protonation of the ketonate rhodium intermediate, deprotonation of the benzamide, and catalyst regeneration, is the most favorable pathway. The 1,2-rhodium migration process can assist decarboxylative activation of vinylene carbonate, which is the rate-determining step in the catalytic cycle. The IRC calculation clearly revealed a quasi-synchronized process to directly afford a cyclic ketonate rhodium intermediate by the release of carbon dioxide.

Published
2024
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34. C6‐Selective Direct Arylation of 2‐Phenylpyridine via an Activated N‐methylpyridinium Salt: A Combined Experimental and Theoretical Study.

Author

Yin, Changzhen, Zhong, Kangbao, Li, Wenjing, Yang, Xiao, Sun, Rui, Zhang, Chunchun, Zheng, Xueli, Yuan, Maolin, Li, Ruixiang, Lan, Yu, Fu, Haiyan, and Chen, Hua

Subjects
*ARYLATION, *IODIDES, *FUNCTIONAL groups, *ELECTRONS, *PYRIDINE
Abstract

An elegant pre‐activation strategy, based on the formation of N‐methylpyridinium iodide salts for C6‐selective direct arylation of 2‐phenylpyridines using Pd/Cu cooperative catalysis, has been developed. By this methodology, a wide range of unsymmetrical 2, 6‐diarylpyridines were synthesized with high reactivity and regioselectivity as well as good functional group tolerance. In particular, challenging substrates bearing electron donating groups (EDGs), such as OMe, NMe2, were also successfully employed in this reaction. Deuterium incorporation studies revealed that the C−H bond acidity is improved significantly in N‐methylpyridinium salts compared with their N‐Oxide and N‐iminopyridinium ylide counterparts, thus solving the long‐standing problem associated with previous strategies for the synthesis of diaryl pyridines. Finally, the control experiments and DFT calculations supported a Pd‐catalyzed and Cu‐mediated mechanism in which a carbenoid copper species that is formed in‐situ from N‐methylpyridinium salts, participates in a Pd‐catalyzed arylation followed by an iodide‐promoted N‐demethylation process. [ABSTRACT FROM AUTHOR]

Published
2018
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35. Is the metal involved or not ? A computational study of Cu(I)-catalyzed [4 + 1] annulation of vinyl indole and carbene precursor

Author

He, Xiaoqian, Zhong, Kangbao, Heng, Dan, Zeng, Zhen, Ni, Hao, Bai, Ruopeng, and Lan, Yu

Abstract

The Cu(I)-catalyzed [4 + 1] annulation of vinyl indoles and a carbene precursor is a powerful method for constructing cyclopentaindole derivatives. Density functional theory (DFT) calculations were used to elucidate the mechanism and regioselectivity of this reaction. After Cu-assisted indole C3-alkylation, direct 1,5-annulation was favored over the Cu-assisted annulation pathway. Furthermore, the regioselectivity for 1,5-annulation was attributed to the generated five-membered-ring product being more stable than the three-membered-ring product from 1,3-annulation, which was the kinetically favored pathway.

Published
2021
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36. Catalyst-Controlled Divergent Generations and Transformations of α-Carbonyl Cations from Alkynes.

Author

Zhou J, Wang W, Zuo F, Liu S, Mosim Amin P, Zhong K, Bai R, and Wang Y

Abstract

α-Carbonyl cations are the umpolung forms of the synthetically fundamental α-carbonyl carbanions. They are highly reactive yet rarely studied and utilized species and their precursors were rather limited. Herein, we report the catalyst-controlled divergent generations of α-carbonyl cations from single alkyne functionalities and the interception of them via Wagner-Meerwein rearrangement. Two chemodivergent catalytic systems have been established, leading to two different types of α-carbonyl cations and, eventually, two different types of products, i.e. the α,β- and β,γ-unsaturated carbonyl compounds. Broad spectrum of alkynes including aryl alkyne, ynamide, alkynyl ether, and alkynyl sulfide could be utilized and the migration priorities of different groups in the Wagner-Meerwein rearrangement step was elucidated. Density functional theory calculations further supported the intermediacy of α-carbonyl cations via the N-O bond cleavage in both the two catalytic systems. Another key feature of this methodology was the fragmentation of synthetically inert tert-butyl groups into readily transformable olefin functionalities. The synthetic potential was highlighted by the scale-up reactions and the downstream diversifications including the formal synthesis of nicotlactone B and galbacin., (© 2023 Wiley-VCH GmbH.)

Published
2023
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37. Revised Mechanism of C(sp 3 )-C(sp 3 ) Reductive Elimination from Ni(II) with the Assistance of a Z-Type Metalloligand.

Author

Zhang T, Zhong K, Lin ZK, Niu L, Li ZQ, Bai R, Engle KM, and Lan Y

Abstract

Reductive elimination is a key step in Ni-catalyzed cross-couplings. Compared with processes that proceed from Ni(III) or Ni(IV) intermediates, C(sp 3 )-C(sp 3 ) reductive eliminations from Ni(II) centers are challenging due to the weak oxidizing ability of Ni(II) species. In this report, we present computational evidence that supports a mechanism in which Zn coordination to the nickel center as a Z-type ligand accelerates reductive elimination. This Zn-assisted pathway is found to be lower in energy compared with direct reductive elimination from a σ-coordinated Ni(II) intermediate, providing new insights into the mechanism of Ni-catalyzed cross-coupling with organozinc nucleophiles. Mayer bond order, Hirshfield charge, Laplacian of the electron density, orbital, and interaction region indicator analyses were conducted to elucidate details of the reductive elimination process and characterize the key intermediates. Theoretical calculations indicate a significant Z-type Ni-Zn interaction that reduces the electron density around the Ni center and accelerates reductive elimination. This mechanistic study of reductive elimination in Ni(0)-catalyzed conjunctive cross-couplings of aryl iodides, organozinc reagents, and alkenes is an important case study of the involvement of Zn-assisted reductive elimination in Ni catalysis. We anticipate that the novel Zn-assisted reductive elimination mode may extend to other cross-coupling processes and explain the unique effectiveness of organozinc nucleophiles in many instances.

Published
2023
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38. Ligand-Controlled Site- and Enantioselective Carbene Insertion into Carbon-Silicon Bonds of Benzosilacyclobutanes.

Author

Huo J, Zhong K, Xue Y, Lyu M, Ping Y, Ouyang W, Liu Z, Lan Y, and Wang J

Abstract

We report herein a highly efficient palladium-catalyzed carbene insertion into strained Si-C bonds of benzosilacyclobutanes, which provides an efficient method to access α-chiral silanes. With a sterically hindered ligand, carbene insertion into the C(sp 3 )-Si bond of benzosilacyclobutanes occurred in excellent site- and enantioselectivity, while C(sp 2 )-Si bond insertion occurred selectively with less sterically hindered ligands. Reaction mechanism, in particular the roles of the chiral ligands in controlling the site-selectivity of the insertion reactions, are elucidated by using hybrid density functional theory., (© 2022 Wiley-VCH GmbH.)

Published
2022
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