- Atroposelective Synthesis of Conjugated Diene-Based Axially Chiral Styrenes via Pd(II)-Catalyzed Thioether-Directed Alkenyl C-H Olefination
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The efficient stereoselective synthesis of conjugated dienes, especially those with axial chirality, remains a great challenge. Herein, we report the highly atroposelective synthesis of axially chiral styrenes with a conjugated 1,3-diene scaffold via a Pd(II)-catalyzed thioether-directed alkenyl C-H olefination strategy. This strategy features easy operation, mild reaction conditions, high functional group tolerance (69 examples), complete Z-selectivity, and excellent enantioselectivities (up to 99% ee). Notably, the highly enantioselective synthesis of atropisomers with two stereogenic axes were also achieved using this strategy (up to 99% ee and 97:3 dr). Moreover, the reaction could be scaled up, and the resulting axially chiral styrenes could be easily oxidized into chiral sulfoxide derivatives with high diastereoselectivities, which showed great promise as a new type of sulfur-olefin ligand.
- Jin, Liang,Zhang, Peng,Li, Ya,Yu, Xin,Shi, Bing-Feng
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supporting information
p. 12335 - 12344
(2021/08/24)
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- Synthesis of Alkenylboronates from N-Tosylhydrazones through Palladium-Catalyzed Carbene Migratory Insertion
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The palladium-catalyzed oxidative borylation reaction of N-tosylhydrazones has been developed. The reaction features mild conditions, broad substrate scope, and good functional group tolerance. It thus represents a highly efficient and practical method for the synthesis of di-, tri-, and tetrasubstituted alkenylboronates from readily available N-tosylhydrazones. One-pot Suzuki coupling and other transformations highlight the synthetic utility of the approach. DFT calculations have revealed that palladium-carbene formation and subsequent boryl migratory insertion are the key steps in the catalytic cycle. The high stereoselectivity observed in the formation of trisubstituted alkenylboronates has been explained by distortion-interaction analysis and NBO analysis.
- Chang, Taiwei,Huo, Jingfeng,Lei, Ming,Ping, Yifan,Wang, Jianbo,Wang, Qianyue,Wang, Rui
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supporting information
p. 9769 - 9780
(2021/07/19)
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- Cobalt-Catalyzed Markovnikov-Type Selective Hydroboration of Terminal Alkynes
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A cobalt-catalyzed Markovnikov-type hydroboration of terminal alkynes with HBpin to access α-alkenyl boronates with good regioselectivity and atom economy is reported. A new ligand has been developed for the cobalt hydride catalyst that has been used for a unique Markovnikov selective insertion of terminal alkynes into metal hydride bond. This operationally simple protocol exhibits excellent functional group tolerance to deliver valuable alkene derivatives.
- Chen, Jieping,Shen, Xuzhong,Lu, Zhan
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supporting information
p. 690 - 694
(2020/11/30)
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- Reaction Pathways and Redox States in α-Selective Cobalt-Catalyzed Hydroborations of Alkynes
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Cobalt(II) alkyl complexes supported by a monoanionic NNN pincer ligand are pre-catalysts for the regioselective hydroboration of terminal alkynes, yielding the Markovnikov products with α:β-(E) ratios of up to 97:3. A cobalt(II) hydride and a cobalt(II) vinyl complex appear to determine the main reaction pathway. In a background reaction the highly reactive hydrido species specifically converts to a coordinatively unsaturated cobalt(I) complex which was found to re-enter the main catalytic cycle.
- Blasius, Clemens K.,Gade, Lutz H.,Matveeva, Regina,Vasilenko, Vladislav,Wadepohl, Hubert
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supporting information
p. 23010 - 23014
(2020/10/20)
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- Rhodium-catalysed diastereo- And enantioselective cyclopropanation of α-boryl styrenes
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A rhodium-catalyzed diastereo- and enantio-selective cyclopropanation of a-boryl styrenes with a-diazoarylacetates was established. Rh2(S-PTTL)4 (0.2 mol%) was found to be effective for the conversion, and 21 diastereopure cyclopropylboronates were prepared in high yields with excellent enantioselectivity (ee up to 99%).
- Sun, Xiao,Gu, Peiming,Qin, Jiao,Su, Yan
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supporting information
p. 12379 - 12382
(2020/10/30)
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- Vinylidene Homologation of Boronic Esters and its Application to the Synthesis of the Proposed Structure of Machillene
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Alkenyl boronic esters are important reagents in organic synthesis. Herein, we report that these valuable products can be accessed by the homologation of boronic esters with lithiated epoxysilanes. Aliphatic and electron-rich aromatic boronic esters provided vinylidene boronic esters in moderate to high yields, while electron-deficient aromatic and vinyl boronic esters were found to give the corresponding vinyl silane products. Through DFT calculations, this divergence in mechanistic pathway has been rationalized by considering the stabilization of negative charge in the C?Si and C?B bond breaking transition states. This vinylidene homologation was used in a short six-step stereoselective synthesis of the proposed structure of machillene, however, synthetic and reported data were found to be inconsistent.
- Fordham, James M.,Grayson, Matthew N.,Aggarwal, Varinder K.
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supporting information
p. 15268 - 15272
(2019/10/21)
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- Cyclodextrin Cavity-Induced Mechanistic Switch in Copper-Catalyzed Hydroboration
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N-heterocyclic carbene-capped cyclodextrin (ICyD) ligands, α-ICyD and β-ICyD derived from α- and β-cyclodextrin, respectively give opposite regioselectivities in a copper-catalyzed hydroboration. The site-selectivity results from two different mechanisms: the conventional parallel one and a new orthogonal mechanism. The shape of the cavity was shown not only to induce a regioselectivity switch but also a mechanistic switch. The scope of interest of the encapsulation of a reactive center is therefore broadened by this study.
- Zhang, Pinglu,Meijide Suárez, Jorge,Driant, Thomas,Derat, Etienne,Zhang, Yongmin,Ménand, Micka?l,Roland, Sylvain,Sollogoub, Matthieu
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supporting information
p. 10821 - 10825
(2017/08/30)
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- Copper-catalyzed regioselective hydroboration of terminal alkynes in aqueous medium
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A mild and environment-friendly copper-catalyzed hydroboration of terminal alkynes in aqueous medium was reported. Regioselectivity control was achieved in the presence of cyclodextrin-bispyridine ligand (CD-1). This protocol was successfully applied to inactivated terminal alkynes. Moreover, the ligand was recovered and reused without any loss of activity over five cycles.
- Yao, Zi-Jian,Hong, Shibin,Zhang, Wei,Liu, Mengyan,Deng, Wei
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supporting information
p. 910 - 913
(2016/02/05)
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