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1.
ChemSusChem ; 2019 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-31804002

RESUMO

The electrolysis of organic acids has garnered increasing attention in recent years. In addition to the famous electrochemical decarboxylation known as Kolbe electrolysis, a number of other electrochemical processes have been recently established that allow for the construction of carbon-heteroatom and sulfur-heteroatom bonds from organic acids. Herein, recent advances in electrochemical C-X and S-X (X=N, O, S, Se) bond-forming reactions from five classes of organic acids and their conjugate bases, namely, carboxylic, thiocarboxylic, phosphonic, sulfinic, and sulfonic acids, are surveyed.

2.
iScience ; 20: 195-204, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31581068

RESUMO

As one of the most promising semiconductor oxide materials, titanium dioxide (TiO2) absorbs UV light but not visible light. To address this limitation, the introduction of Ti3+ defects represents a common strategy to render TiO2 visible-light responsive. Unfortunately, current hurdles in Ti3+ generation technologies impeded the widespread application of Ti3+ modified materials. Herein, we demonstrate a simple and mechanistically distinct approach to generating abundant surface-Ti3+ sites without leaving behind oxygen vacancy and sacrificing one-off electron donors. In particular, upon adsorption of organodiboron reagents onto TiO2 nanoparticles, spontaneous electron injection from the diboron-bound O2- site to adjacent Ti4+ site leads to an extremely stable blue surface Ti3+‒O-· complex. Notably, this defect generation protocol is also applicable to other semiconductor oxides including ZnO, SnO2, Nb2O5, and In2O3. Furthermore, the as-prepared photoelectronic device using this strategy affords 103-fold higher visible light response and the fabricated perovskite solar cell shows an enhanced performance.

3.
Langmuir ; 35(44): 14173-14179, 2019 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-31411486

RESUMO

ZnO semiconductor oxides are versatile functional materials that are used in photoelectronics, catalysis, sensing, etc. The Zn+-O- surface electronic states of semiconductor oxides were formed on the ZnO surface by Zn 4s and O 2p orbital coupling with the diboron compound's B 2p orbitals. The formation of spin-coupled surface states was based on the spin-orbit interaction on the interface, which has not been reported before. This shows that the semiconductor oxide's spin surface states can be modulated by regulating surface orbital energy. The Zn+-O- surface electronic states were confirmed by electron spin resonance results, which may help in expanding the fundamental research on spintronics modulation and quantum transport.

4.
Org Lett ; 2019 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-31247743

RESUMO

We describe an operationally simple transition-metal-free borylation of alkyl iodides. This method uses commercially available diboron reagents as the boron source and exhibits excellent functional group compatibility. Furthermore, a diverse range of primary and secondary alkyl iodides could be effectively transformed to the corresponding alkylboronates in excellent yield. Mechanistic investigations suggest that this borylation reaction proceeds through a single-electron transfer mechanism featuring the generation of an alkyl radical intermediate.

5.
Org Lett ; 21(3): 762-766, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30672710

RESUMO

A general electrohemical strategy for the combined trifluoromethylation/C(sp2)-H functionalization using Langlois' reagent as the CF3 source under oxidant-free conditions was developed. Using Mn salts as the redox mediator, this method provides an efficient and sustainable means to access a variety of functionalized heterocycles bearing a CF3 moiety. Detailed mechanistic studies are consistent with the formation of CF3-bound high oxidation state Mn species, suggesting a transition-metal-mediated CF3 transfer mechanism for this trifluoromethylation/C(sp2)-H functionalization process.

6.
ChemSusChem ; 12(1): 6-39, 2019 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-30381905

RESUMO

Carbon dioxide is a nontoxic, renewable, and abundant C1 source, whereas C-H bond functionalization represents one of the most important approaches to the construction of carbon-carbon bonds and carbon-heteroatom bonds in an atom- and step-economical manner. Combining the chemical transformation of CO2 with C-H bond functionalization is of great importance in the synthesis of carboxylic acids and their derivatives. The contents of this Review are organized according to the type of C-H bond involved in carboxylation. The primary types of C-H bonds are as follows: C(sp)-H bonds of terminal alkynes, C(sp2 )-H bonds of (hetero)arenes, vinylic C(sp2 )-H bonds, the ipso-C(sp2 )-H bonds of the diazo group, aldehyde C(sp2 )-H bonds, α-C(sp3 )-H bonds of the carbonyl group, γ-C(sp3 )-H bonds of the carbonyl group, C(sp3 )-H bonds adjacent to nitrogen atoms, C(sp3 )-H bonds of o-alkyl phenyl ketones, allylic C(sp3 )-H bonds, C(sp3 )-H bonds of methane, and C(sp3 )-H bonds of halogenated aliphatic hydrocarbons. In addition, multicomponent reactions, tandem reactions, and key theoretical studies related to the carboxylation of C-H bonds are briefly summarized. Transition-metal-free, organocatalytic, electrochemical, and light-driven methods are highlighted.

7.
Adv Mater ; 30(49): e1805085, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30294817

RESUMO

Metal halide perovskite films are endowed with the nature of ions and polycrystallinity. Formamidinium iodide (FAI)-based perovskite films, which include large cations (FA) incorporated into the crystal lattice, are most likely to induce local defects due to the presence of the unreacted FAI species. Here, a diboron-assisted strategy is demonstrated to control the defects induced by the unreacted FAI both inside the grain boundaries and at the surface regions. The diboron compound (C12 H10 B2 O4 ) can selectively react with unreacted FAI, leading to reduced defect densities. Nonradiative recombination between a perovskite film and a hole-extraction layer is mitigated considerably after the introduction of the proposed approach and charge-carrier extraction is improved as well. A champion power conversion efficiency of 21.11% is therefore obtained with a stabilized power output of 20.83% at the maximum power point for planar perovskite solar cells. The optimized device also delivers negligible hysteresis effect under various scanning conditions. This approach paves a new way for mitigating defects and improving device performance.

8.
J Org Chem ; 83(7): 4275-4278, 2018 04 06.
Artigo em Inglês | MEDLINE | ID: mdl-29552885

RESUMO

We describe here an operationally simple and straightforward synthesis method for a series of diverse 4,5-disubstituted 1,2,3-thiadiazoles via the nucleophilic addition of α-diazo carbonyl compounds to carbon disulfide. This method features using abundant and inexpensive carbon disulfide under mild reaction conditions.

9.
J Org Chem ; 83(6): 3200-3207, 2018 03 16.
Artigo em Inglês | MEDLINE | ID: mdl-29471627

RESUMO

An anodic oxidation/cyclization of 2-arylbenzoic acids for the synthesis of dibenzopyranones has been developed. The reaction proceeds at room temperature with no oxidant or electrolyte required and exhibits a high atom economy with H2 being the only byproduct. A series of dibenzopyranones was obtained in good to excellent yields. Urolithins A, B, and C are formally synthesized by adopting this method as a key step to demonstrate its synthetic utility.

10.
Acc Chem Res ; 51(2): 496-506, 2018 02 20.
Artigo em Inglês | MEDLINE | ID: mdl-29368912

RESUMO

The Sandmeyer reaction represents an important organic transformation that converts an arylamine to an aryl halide using Cu(I) halide via a diazonium salt intermediate. The reaction was first reported by Sandmeyer in 1884, and a number of named reactions closely related to it have been developed and widely applied in organic synthesis throughout the 20th century. These include the Pschorr reaction for the synthesis of biaryl tricycles, the Gomberg-Bachmann reaction for biaryl formations, the Balz-Schiemann reaction for C-F bond formations, and the Meerwein reaction for arylation of α,ß-unsaturated carbonyl compounds. However, all these reactions were discovered before 1940. In 1977, Doyle and co-workers reported an organic phase diazotization process, and Kikukawa and Matsuda used aryldiazonium salts in transition metal-catalyzed cross-coupling reactions. However, completely new processes involving diazonium salts have been seldom reported since then, although aryldiazonium salts are widely utilized in modern organic synthesis. In the past few years, diazonium salt chemistry has been revisited and become a fast-growing research topic. Several novel transformations based on diazonium salts have been developed and have been practiced in organic synthesis. In 2010, we reported a direct conversion of arylamines to pinacol boronates through the reaction of in situ generated aryl diazonium salts with B2pin2. This new strategy is under metal-free conditions and thus completely avoids contamination by transition metals in the boron products. From readily available arylamines various functionalized arylboronates, some of which are difficult to access by other methods, can be easily obtained with this reaction. Mechanistic investigations indicate the reaction likely follows a radical mechanism, which is similar to traditional Sandmeyer-type reactions. Subsequently, modified reaction conditions for this transformation appeared in the literature, which include light-induced reactions, aqueous-phase diazotization methods, and reactions with aryltriazenes as the arene diazonium salt surrogates. In addition to the borylation, we have also demonstrated the corresponding stannylation and phosphorylation of arylamines with similar Sandmeyer-type approaches. The stannylation of arylamines was achieved by the reaction of in situ generated diazonium salts with a distannane reagent, while phosphorylation is the reaction of arylamines with trimethyl phosphite in the presence of tert-butyl nitrite (t-BuONO). With the sequential borylation and stannylation approaches, the aromatic compounds bearing two amino groups are easily converted into trimethylstannyl arylboronates, which can be further used in consecutive Stille and Suzuki-Miyaura cross-couplings. Finally, direct conversion of the amino group of arylamines to the trifluoromethyl group has been developed through aryl diazonium salts almost simultaneously by several groups. These reactions represent a novel strategy to achieve trifluoromethylation of aromatic compounds. These developments show the revivification of this age-old chemistry, and this Account will summarize the Sandmeyer reaction-related transformations that have been developed since 2010.

11.
Chem Sci ; 9(46): 8731-8737, 2018 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-30627393

RESUMO

Herein we report a general electrochemical strategy for the Sandmeyer reaction. Using electricity as the driving force, this protocol employs a simple and inexpensive halogen source, such as NBS, CBrCl3, CH2I2, CCl4, LiCl and NaBr for the halogenation of aryl diazonium salts. In addition, we found that these electrochemical reactions could be performed using anilines as the starting material in a one-pot fashion. Furthermore, the practicality of this process was demonstrated in the multigram scale synthesis of aryl halides using highly inexpensive graphite as the electrode. A series of detailed mechanism studies have been performed, including radical clock and radical scavenger study, cyclic voltammetry analysis and in situ electron paramagnetic resonance (EPR) analysis.

12.
Org Lett ; 19(24): 6756-6759, 2017 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-29210276

RESUMO

The direct carboxylation of the ipso-C(sp2)-H bond of a diazo compound with carbon dioxide under mild reaction conditions is described. This method is transition-metal-free, uses a weak base, and proceeds at ambient temperature under atmospheric pressure in carbon dioxide. The carboxylation exhibits high reactivity and is amenable to subsequent diversification. A series of unsymmetrical 1,3-diester/keto/amide diazo compounds are obtained with moderate to excellent yields (up to 99%) with good functional group compatibility.

13.
Angew Chem Int Ed Engl ; 55(49): 15401-15405, 2016 12 05.
Artigo em Inglês | MEDLINE | ID: mdl-27862772

RESUMO

The rhodium(I)-catalyzed C-C bond activation reaction of siloxyvinylcyclopropanes with diazoesters demonstrates a novel mode of C-C bond cleavage of siloxyvinvylcyclopanes. The alkene products were obtained as single E-configured isomers in good yields. A σ,η3 -allyl rhodium complex, which has been previously proposed as the key intermediate in rhodium(I)-catalyzed cycloaddition of vinylcyclopropanes, has been isolated and characterized by X-ray crystallography.

14.
J Am Chem Soc ; 138(44): 14558-14561, 2016 11 09.
Artigo em Inglês | MEDLINE | ID: mdl-27788320

RESUMO

A highly enantioselective synthesis of trisubstituted allenes has been achieved through Cu(I)-catalyzed cross-coupling of aryldiazoalkanes and terminal alkynes with chiral bisoxazoline ligands. Alkynyl migratory insertion of Cu(I) carbene is proposed as the key step for the construction of axial chirality.

15.
J Org Chem ; 81(23): 11603-11611, 2016 12 02.
Artigo em Inglês | MEDLINE | ID: mdl-27792351

RESUMO

An efficient metal-free phosphorylation process based on a Sandmeyer-type transformation with arylamines as the starting materials is developed. The transformation proceeds smoothly at room temperature without the exclusion of moisture or air. This phosphorylation reaction tolerates a wide range of functional groups and affords the phosphorylation products in moderate to good yields, thus providing a valuable method for the formation of aromatic carbon-phosphorus bonds.

16.
J Am Chem Soc ; 137(49): 15518-27, 2015 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-26565679

RESUMO

Here, we describe a detailed study of the rhodium(I)-catalyzed, bifunctional ligand-assisted ketone α-C-H alkenylation using internal alkynes. Through controlling the reaction conditions, conjugated enamines, α,ß- or ß,γ-unsaturated ketones, can be selectively accessed. Both aromatic and aliphatic alkynes can be employed as coupling partners. The reaction conditions also tolerate a broad range of functional groups, including carboxylic esters, malonates, secondary amides, thioethers, and free alcohols. In addition, excellent E-selectivity was observed for the tetra-substituted alkene when forming the α,ß-unsaturated ketone products. The mechanism of this transformation was explored through control experiments, kinetic monitoring, synthesizing the rhodium-hydride intermediates and their reactions with alkynes, deuterium-labeling experiments, and identification of the resting states of the catalyst.

17.
Chem Soc Rev ; 44(21): 7764-86, 2015 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-26185960

RESUMO

Transition metal-catalyzed C-H functionalization has evolved into a prominent and indispensable tool in organic synthesis. While nitrogen, phosphorus and sulfur-based functional groups (FGs) are widely employed as effective directing groups (DGs) to control the site-selectivity of C-H activation, the use of common FGs (e.g. ketone, alcohol and amine) as DGs has been continuously pursued. Ketones are an especially attractive choice of DGs and substrates due to their prevalence in various molecules and versatile reactivity as synthetic intermediates. Over the last two decades, transition metal-catalyzed C-H functionalization that is directed or mediated by ketones has experienced vigorous growth. This review summarizes these advancements into three major categories: use of ketone carbonyls as DGs, direct ß-functionalization, and α-alkylation/alkenylation with unactivated olefins and alkynes. Each of these subsections is discussed from the perspective of strategic design and reaction discovery.

18.
Chemistry ; 21(19): 7082-98, 2015 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-25877472

RESUMO

Lewis base adducts of tetra-alkoxy diboron compounds, in particular bis(pinacolato)diboron (B2 pin2 ), have been proposed as the active source of nucleophilic boryl species in metal-free borylation reactions. We report the isolation and detailed structural characterization (by solid-state and solution NMR spectroscopy and X-ray crystallography) of a series of anionic adducts of B2 pin2 with hard Lewis bases, such as alkoxides and fluoride. The study was extended to alternative Lewis bases, such as acetate, and other diboron reagents. The B(sp(2) )-B(sp(3) ) adducts exhibit two distinct boron environments in the solid-state and solution NMR spectra, except for [(4-tBuC6 H4 O)B2 pin2 ](-) , which shows rapid site exchange in solution. DFT calculations were performed to analyze the stability of the adducts with respect to dissociation. Stoichiometric reaction of the isolated adducts with two representative series of organic electrophiles-namely, aryl halides and diazonium salts-demonstrate the relative reactivities of the anionic diboron compounds as nucleophilic boryl anion sources.


Assuntos
Compostos de Boro/química , Ânions/síntese química , Ânions/química , Compostos de Boro/síntese química , Cristalografia por Raios X , Compostos de Diazônio/síntese química , Compostos de Diazônio/química , Fluoretos/síntese química , Fluoretos/química , Halogenação , Bases de Lewis/síntese química , Bases de Lewis/química
19.
J Org Chem ; 80(2): 1221-8, 2015 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-25536149

RESUMO

We describe cholate-based cage amphiphiles with a unique architecture that combines elements of structural rigidity and flexibility. The cage compounds are built by extending and bridging three polar chains underneath the concave steroid rings of cholate and capping with another rigid, symmetrically trifunctionalized cyanuric acid moiety. The connecting chains are varied to include, for instance, oligo(ethylene glycol) or chains containing 1,2,3-triazole units to present flexibility in the chemical and structural space and potentially deliver functional molecules for molecular recognition applications.


Assuntos
Colatos/química , Etilenoglicol/química , Triazóis/química , Estrutura Molecular
20.
Science ; 345(6192): 68-72, 2014 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-24994648

RESUMO

Alkylation of carbonyl compounds is a commonly used carbon-carbon bond-forming reaction. However, the conventional enolate alkylation approach remains problematic due to lack of regioselectivity, risk of overalkylation, and the need for strongly basic conditions and expensive alkyl halide reagents. Here, we describe development of a ketone-alkylation strategy using simple olefins as the alkylating agents. This strategy employs a bifunctional catalyst comprising a secondary amine and a low-valent rhodium complex capable of activating ketones and olefins simultaneously. Both cyclic and acyclic ketones can be mono-α-alkylated with simple terminal olefins, such as ethylene, propylene, 1-hexene, and styrene, selectively at the less hindered site; a large number of functional groups are tolerated. The pH/redox neutral and byproduct-free nature of this dual-activation approach shows promise for large-scale syntheses.

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