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1.
Nat Commun ; 10(1): 949, 2019 02 27.
Artigo em Inglês | MEDLINE | ID: mdl-30814517

RESUMO

Transition-metal-catalyzed cycloisomerization of 1,n-allenynes represents a powerful synthetic tool to rapidly assemble complex polycyclic skeletons from simple linear substrates. Nevertheless, there are no reports of the asymmetric version of these reactions. Moreover, most of these reactions proceed through a 6-endo-dig cyclization pathway, which preferentially delivers the distal product (via 5/5 rhodacyclic intermediate) rather than the proximal one (via 6/5 rhodacyclic intermediate). Herein, we report an enantioselective rhodium(I)-catalyzed cycloisomerization of 1,6-allenynes to provide the proximal product 5/6-fused bicycle[4.3.0]nonadienes in good yields and with excellent enantioselectivities. Remarkably, this chemistry works perfectly for 1,6-allenynes having a cyclic substituent within the allene component, thereby affording synthetically formidable tricyclic products with excellent enantioselectivities. Moreover, extensive DFT calculations suggest an uncommon pathway involving 5-exo-dig cycloisomerization, ring-expansion, rate-determining alkene isomerization involving Csp3-H activation, C-C activation of the cyclobutene moiety and finally reductive elimination. Deuterium labeling experiments support the rate-determining step involving the C-H bond activation in this transformation.

2.
J Am Chem Soc ; 141(7): 2872-2877, 2019 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-30721058

RESUMO

The first asymmetric total synthesis of the highly strained compound cerorubenic acid-III is reported. A type II intramolecular [5 + 2] cycloaddition allowed efficient and diastereoselective construction of the synthetically challenging bicyclo[4.4.1] ring system with a strained bridgehead (anti-Bredt) double bond in the final product. A unique transannular cyclization installed the vinylcyclopropane moiety with retention of the desired stereochemistry.

3.
Adv Mater ; 31(15): e1805944, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30697836

RESUMO

Molecular doping of inorganic semiconductors is a rising topic in the field of organic/inorganic hybrid electronics. However, it is difficult to find dopant molecules which simultaneously exhibit strong reducibility and stability in ambient atmosphere, which are needed for n-type doping of oxide semiconductors. Herein, successful n-type doping of SnO2 is demonstrated by a simple, air-robust, and cost-effective triphenylphosphine oxide molecule. Strikingly, it is discovered that electrons are transferred from the R3P+ O- σ-bond to the peripheral tin atoms other than the directly interacted ones at the surface. That means those electrons are delocalized. The course is verified by multi-photophysical characterizations. This doping effect accounts for the enhancement of conductivity and the decline of work function of SnO2 , which enlarges the built-in field from 0.01 to 0.07 eV and decreases the energy barrier from 0.55 to 0.39 eV at the SnO2 /perovskite interface enabling an increase in the conversion efficiency of perovskite solar cells from 19.01% to 20.69%.

4.
Org Lett ; 21(2): 360-364, 2019 01 18.
Artigo em Inglês | MEDLINE | ID: mdl-30600680

RESUMO

Hydrogenation catalyzed by unusually low-valent Co(-I) and Fe(-I) catalysts were recently reported. In contrast to the classical M(I)/M(III) (M = Rh or Ir) or Ir(III)/Ir(V) catalytic cycles in the singlet state (adiabatic reactions) for Rh- or Ir-catalyzed hydrogenation, our systematic DFT study elucidates a new Co(-I)/Co(0)/Co(+I) catalytic cycle involving both singlet and triplet states (nonadiabatic reaction). Also, the more electron-rich cobalt center of the Co(-I) catalyst was found to contribute higher reactivity for alkene hydrogenation.

6.
Nat Commun ; 9(1): 2045, 2018 05 23.
Artigo em Inglês | MEDLINE | ID: mdl-29795178

RESUMO

Hydroformylation of 1,2-disubstituted alkenes usually occurs at the α position of the directing heteroatom such as oxygen atom and nitrogen atom. By contrast, to achieve hydroformylation on the ß position of the heteroatom is a tough task. Herein, we report the asymmetric rhodium-catalyzed hydroformylation of 1,2-disubstituted alkenylsilanes with excellent regioselectivity at the ß position (relative to the silicon heteroatom) and enantioselectivity. In a synthetic sense, we achieve the asymmetric hydroformylation on the ß position of the oxygen atom indirectly by using the silicon group as a surrogate for the hydroxyl. Density functional theory (DFT) calculations are carried out to examine energetics of the whole reaction path for Rh/YanPhos-catalyzed asymmetric hydroformylation and understand its regioselectivity and enantioselectivity. Our computational study suggests that the silicon group can activate the substrate and is critical for the regioselectivity.

7.
Chem Sci ; 9(7): 1919-1924, 2018 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-29675238

RESUMO

With the assistance of hydrogen bonds, the first asymmetric hydrogenation of ß-cyanocinnamic esters is developed, affording chiral ß-cyano esters with excellent enantioselectivities (up to 99% ee). This novel methodology provides an efficient and concise synthetic route to chiral GABA-derivatives such as (S)-Pregabalin, (R)-Phenibut, (R)-Baclofen. Interestingly, in this system, the catalyst with a single H-bond donor performs better than that with double H-bond donors, which is a novel discovery in the metalorganocatalysis area.

8.
Chem Commun (Camb) ; 54(36): 4581-4584, 2018 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-29667658

RESUMO

Although recent progress has been made in introducing an SCF3 functionality into a variety of molecules, enantioselective trifluoromethylthiolation remains challenging, especially the α-trifluoromethylthiolation of carbonyl compounds. The present study describes a diastereo and enantioselective Cu-catalyzed tandem 1,4-addition/trifluoromethylthiolation of acyclic enones. The tandem reaction enables the asymmetric integration of the -SCF3 group to carbonyl compounds, establishing chiral tertiary α-carbon centers and affording α-SCF3-ß-substituted carbonyl compounds in 50-92% yields with up to 20 : 1 dr and 96% ee.

9.
Org Lett ; 20(8): 2143-2147, 2018 04 20.
Artigo em Inglês | MEDLINE | ID: mdl-29600702

RESUMO

The incorporation of Brønsted acid, thiourea anion binding, and transition metal catalysis enables an efficient method to synthesize chiral indolines via hydrogenation of indoles. Catalyzed by a rhodium/ZhaoPhos complex, asymmetric hydrogenation of unprotected indoles is performed smoothly with excellent enantioselectivities (up to 99% ee, up to 400 TON). Brønsted acid HCl activates indoles to form iminium ion intermediates. Mechanistic studies support the assumption that anion binding plays a crucial role as a secondary interaction. DFT calculations reveal an outer-sphere mechanism in this chemical transformation.

10.
J Am Chem Soc ; 140(15): 4977-4981, 2018 04 18.
Artigo em Inglês | MEDLINE | ID: mdl-29601724

RESUMO

A series of novel hybrid phosphorus ligands were designed and applied to the Rh-catalyzed enantioselective anti-Markovnikov hydroformylation of unfunctionalized 1,1-disubstituted alkenes. By employing the new catalyst, linear aldehydes with ß-chirality can be prepared with high yields and enantioselectivities under mild conditions. Furthermore, catalyst loading as low as 0.05 mol % furnished the desired product in good yield and undiminished selectivity, demonstrating the efficiency of this transformation in large-scale synthesis.

11.
Chem Commun (Camb) ; 54(5): 535-538, 2018 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-29271428

RESUMO

A secondary phosphine oxide-phosphine mixed tridentate ligand and its ruthenium complex have been developed. This complex shows excellent catalytic activity for carbonyl reduction, especially for the reduction of α,ß-unsaturated aldehydes. The turnover number and selectivity can reach up to 36 500 and 99%, respectively. Control experiments and DFT calculations supported an outer-sphere mechanism during the hydrogenation reaction.

12.
iScience ; 11: 146-159, 2018 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-30612034

RESUMO

Development of a general catalytic and highly efficient method utilizing readily available precursors for the regio- and stereoselective construction of bioactive natural-product-inspired spiro architectures remains a formidable challenge in chemical research. Transition metal-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides produces numerous N-heterocycles, but reaction control with the regioselectivity opposite to the conventional fashion has rarely been demonstrated. Herein, we report a unique ligand-controlled Cu(I)-catalyzed umpolung-type 1,3-dipolar cycloaddition of azomethine ylide to realize efficient kinetic resolution of racemic alkylidene norcamphors with the concomitant construction of previously inaccessible spiro N-heterocycles with high levels of regio- and stereoselectivity. The success of this methodology relies on the strategy of kinetic resolution, and the serendipitous discovery of a unique ligand-enabled regiospecific cycloaddition, which not only provides evidence for the existence of the minor zwitterionic resonance form in metallated azomethine ylide but also diversifies the existing chemistry of azomethine ylide-involved 1,3-dipolar cycloadditions with rare polarity inversion.

13.
Chem Sci ; 8(9): 6419-false, 2017 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-29163927

RESUMO

An efficient approach for synthesizing chiral ß-amino nitroalkanes has been developed via the Ni-catalyzed asymmetric hydrogenation of challenging ß-amino nitroolefins under mild conditions, affording the desired products in excellent yields and with high enantioselectivities. This protocol had good compatibility with the wide substrate scope and a range of functional groups. The synthesis of chiral ß-amino nitroalkanes on a gram scale has also been achieved. In addition, the reaction mechanism was elucidated using a combined experimental and computational study, and it involved acetate-assisted heterolytic H2 cleavage followed by 1,4-hydride addition and protonation to achieve the nitroalkanes.

14.
Chem Sci ; 8(9): 6247-6256, 2017 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-28989658

RESUMO

Polycyclic alkaloids bearing all-carbon quaternary centers possess a diversity of biological activities and are challenging targets in natural product synthesis. The development of a general and asymmetric catalytic method applicable to the efficient syntheses of a series of complex polycyclic alkaloids remains highly desirable in synthetic chemistry. Herein we describe an efficient palladium-catalyzed enantioselective dearomative cyclization which is capable of synthesizing two important classes of tricyclic nitrogen-containing skeleton, chiral dihydrophenanthridinone and dihydrocarbazolone derivatives bearing all-carbon quaternary centers, in excellent yields and enantioselectivities. The P-chiral monophosphorus ligand AntPhos is crucial for the reactivity and enantioselectivity, and the choice of the N-phosphoramide protecting group is essential for the desired chemoselectivity. This method has enabled the enantioselective total syntheses of three distinctive and challenging biologically important polycyclic alkaloids, specifically a concise and gram-scale synthesis of (-)-crinine, an efficient synthesis of indole alkaloid (-)-aspidospermidine and a formal enantioselective synthesis of (-)-minfiensine.

15.
Chem Sci ; 8(7): 5161-5165, 2017 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-28970901

RESUMO

A practical and enantioselective palladium-catalyzed diboration of 1,1-disubstituted allenes is developed by employing a P-chiral monophosphorus ligand, BI-DIME. A series of diboronic esters containing a chiral tertiary boronic ester moiety are formed in excellent yields and ee's with the palladium loading as low as 0.2 mol%. DFT calculations revealed a concerted mechanism of oxidative addition of bis(pinacolato)diboron and allene insertion, as well as a critical dispersion effect on the origins of the enantioselectivity. The method is successfully applied to the concise and enantioselective synthesis of brassinazole.

16.
J Am Chem Soc ; 139(46): 16438-16441, 2017 11 22.
Artigo em Inglês | MEDLINE | ID: mdl-29037035

RESUMO

The photoinduced Zimmerman di-π-methane (DPM) rearrangement of polycyclic molecules to form synthetically useful cyclopropane derivatives was found experimentally to proceed in a triplet excited state. We have applied state-of-the-art quantum mechanical methods, including M06-2X, DLPNO-CCSD(T) and variational transition-state theory with multidimensional tunneling corrections, to an investigation of the reaction rates of the two steps in the triplet DPM rearrangement of dibenzobarrelene, benzobarrelene and barrelene. This study predicts a high probability of carbon tunneling in regions around the two consecutive transition states at 200-300 K, and an enhancement in the rates by 104-276/35-67% with carbon tunneling at 200/300 K. The Arrhenius plots of the rate constants were found to be curved at low temperatures. Moreover, the computed 12C/13C kinetic isotope effects were affected significantly by carbon tunneling and temperature. Our predictions of electronically excited-state carbon tunneling and two consecutive carbon tunneling are unprecedented. Heavy-atom tunneling in some photoinduced reactions with reactive intermediates and narrow barriers can be potentially observed at relatively low temperature in experiments.

17.
J Am Chem Soc ; 139(29): 9767-9770, 2017 07 26.
Artigo em Inglês | MEDLINE | ID: mdl-28700227

RESUMO

We herein describe a chiral diboron-templated highly diastereoselective and enantioselective reductive coupling of isoquinolines that provided expedited access to a series of chiral substituted bisisoquinolines in good yields and excellent ee's under mild conditions. The method enjoys a broad substrate scope and good functional group compatibility. Mechanistic investigation suggests the reaction proceeds through a concerted [3,3]-sigmatropic rearrangement.

18.
Nat Commun ; 8: 16119, 2017 06 27.
Artigo em Inglês | MEDLINE | ID: mdl-28653676

RESUMO

This corrects the article DOI: 10.1038/ncomms15238.

19.
Inorg Chem ; 56(12): 6809-6819, 2017 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-28558249

RESUMO

A dinuclear, Cu(I)-catalyzed reductive CO2 coupling reaction was recently developed to selectively yield a metal-oxalate product through electrochemical means, instead of the usual formation of carbonate and CO ( Science 2010 , 327 , 313 ). To shed light on the mechanism of this important and unusual reductive coupling reaction, extensive and systematic density functional theory (DFT) calculations on several possible pathways and spin states were performed in which a realistic system up to 164 atoms was adopted. Our calculations support the observation that oxalate formation is energetically more favorable than the formation of carbonate and CO products in this cationic Cu(I) complex. Spatial confinement of the realistic catalyst (a long metal-metal distance) was found to further destabilize the carbonate formation, whereas it slightly promotes oxalate formation. Our study does not support the proposed diradical coupling mechanism. Instead, our calculations suggest a new mechanism in which one CO2 molecule is first reduced cooperatively by two Cu(I) metals to give a new, fully delocalized mixed-valence Cu2I/II(CO2•-) radical anion intermediate (analogues to Type 4 Cu center, CuA), followed by further partial reduction of the metal-ligated CO2 molecule and (metal-mediated) nucleophilic-like attack on the carbon atom of an incoming second CO2 molecule to afford the dinuclear Cu(II)-oxalate product. Overall, our proposed reaction mechanism involves a closed-shell reactant as well as two open-shell transition states and products. The effects of size, charge, and catalyst metal on the oxalate formation were also investigated and compared.

20.
Angew Chem Int Ed Engl ; 56(24): 6808-6812, 2017 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-28493501

RESUMO

Inspired by the unique character of enzymes, we developed novel chiral SPO (secondary-phosphine-oxide) ligand (SPO-Wudaphos) which can enter into both ion pair and H-bond noncovalent interactions. The novel chiral SPO-Wudaphos exhibited excellent results in the asymmetric hydrogenation of α-methylene-γ-keto carboxylic acids, affording the chiral γ-keto acids with up to over 99 % ee. A series of control experiments and DFT calculations were conducted to illustrate the critical roles of both the ion pair and H-bond noncovalent interactions.

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