scholarly journals Unconventional mechanism and selectivity of the Pd-catalyzed C–H bond lactonization in aromatic carboxylic acid

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Li-Ping Xu ◽  
Shaoqun Qian ◽  
Zhe Zhuang ◽  
Jin-Quan Yu ◽  
Djamaladdin G. Musaev

AbstractThe search for more effective and highly selective C–H bond oxidation of accessible hydrocarbons and biomolecules is a greatly attractive research mission. The elucidating of mechanism and controlling factors will, undoubtedly, help to broaden scope of these synthetic protocols, and enable discovery of more efficient, environmentally benign, and highly practical new C–H oxidation reactions. Here, we reveal the stepwise intramolecular SN2 nucleophilic substitution mechanism with the rate-limiting C–O bond formation step for the Pd(II)-catalyzed C(sp3)–H lactonization in aromatic 2,6-dimethylbenzoic acid. We show that for this reaction, the direct C–O reductive elimination from both Pd(II) and Pd(IV) (oxidized by O2 oxidant) intermediates is unfavorable. Critical factors controlling the outcome of this reaction are the presence of the η3-(π-benzylic)–Pd and K+–O(carboxylic) interactions. The controlling factors of the benzylic vs ortho site-selectivity of this reaction are the: (a) difference in the strains of the generated lactone rings; (b) difference in the strengths of the η3-(π-benzylic)–Pd and η2-(π-phenyl)–Pd interactions, and (c) more pronounced electrostatic interaction between the nucleophilic oxygen and K+ cation in the ortho-C–H activation transition state. The presented data indicate the utmost importance of base, substrate, and ligand in the selective C(sp3)–H bond lactonization in the presence of C(sp2)–H.

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.


2021 ◽  
Vol 23 (35) ◽  
pp. 19280-19288
Author(s):  
Nhu Pailes Nguyen ◽  
Tyler P. Farr ◽  
H. Evan Bush ◽  
Andrea Ambrosini ◽  
Peter G. Loutzenhiser

Two-step solar thermochemical cycles based on reversible reactions of SrFeO3−δ and (Ba,La)0.15Sr0.85FeO3−δ perovskites were considered for air separation.


ACS Catalysis ◽  
2021 ◽  
pp. 10479-10486
Author(s):  
Jeremy D. Griffin ◽  
David B. Vogt ◽  
J. Du Bois ◽  
Matthew S. Sigman

2020 ◽  
Vol 22 (3) ◽  
pp. 895-902
Author(s):  
Xueli Bai ◽  
Nianze Song ◽  
Liang Wen ◽  
Xin Huang ◽  
Jian Zhang ◽  
...  

It is significant for the environment that molecular oxygen replaces conventional heavy metal-containing or toxic oxidants to participate in oxidation reactions.


2013 ◽  
Vol 68 (5-6) ◽  
pp. 587-597 ◽  
Author(s):  
Bo Zhang ◽  
Su Li ◽  
Alexander Pöthig ◽  
Mirza Cokoja ◽  
Shu-Liang Zang ◽  
...  

Ionic compounds containing the polyoxomolybdate anion [Mo6O19]2- and [(n-C4H9)4P]+ (tetrabutylphosphonium), [(n-C4H9)3P(n-C14H29)]+ (tributyl (tetradecyl)phosphonium), [Bmim]+ (1- butyl-3-methylimidazolium) and [Dbmim]+ (1,2-dimethyl-3-butylimidazolium) cations were prepared and characterized, including the determination of three of the solid state structures by singlecrystal X-ray diffraction. These compounds were applied as catalysts for the epoxidation of olefins with urea hydrogen peroxide (UHP) as oxidant in the ionic liquid [Bmim]PF6. Additionally, the oxidation of sulfides to sulfoxides with hydrogen peroxide (H2O2) in several solvents was investigated. The polyoxomolybdate catalysts showed a good performance for epoxidation of olefins as well as for oxidation of sulfides. Furthermore, the catalysts can be recycled several times in oxidation reactions. We present this methodology for the oxidation reaction in a simple, economically, technically, and environmentally benign manner


1999 ◽  
Vol 19 (12) ◽  
pp. 8094-8102 ◽  
Author(s):  
Kefei Yu ◽  
Michael R. Lieber

ABSTRACT V(D)J recombination is directed by recombination signal sequences. However, the flanking coding end sequence can markedly affect the frequency of the initiation of V(D)J recombination in vivo. Here we demonstrate that the coding end sequence effect can be qualitatively and quantitatively recapitulated in vitro with purified RAG proteins. We find that coding end sequence specifically affects the nicking step, which is the first biochemical step in RAG-mediated cleavage. The subsequent hairpin formation step is not affected by the coding end sequence. Furthermore, the coding end sequence effect can be ablated by prenicking the substrate, indicating that the coding end effect is specific to the nicking step. In reactions in which both 12- and 23-substrates are present, a suboptimal coding end sequence on one signal can slow down hairpin formation at the partner signal, a result consistent with models in which coordination between the signals occurs at the hairpin formation step. The coding end sequence effect on nicking and the coupling of the 12- and 23-substrates explains how hairpin formation can be rate limiting for some 12/23 pairs, whereas nicking can be rate limiting when low-efficiency coding end sequences are involved.


2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.


2000 ◽  
Vol 72 (7) ◽  
pp. 1273-1287 ◽  
Author(s):  
Wolfgang F. Hoelderich ◽  
Felix Kollmer

This review outlines several approaches for designing new and environmentally friendly heterogeneously catalyzed oxidation processes for the synthesis of fine and intermediate chemicals. Environmentally benign oxidants such as molecular oxygen, hydrogen peroxide or nitrous oxide can be activated on suitable heterogeneous catalysts showing high activity and selectivity toward the desired oxygenated products. Several examples illustrate that features known from the synthesis of bulk chemicals can successfully be applied for manufacturing intermediate and specialty chemicals applying conventional industrial reactor systems. Direct oxidation of isoprenol, b-picoline, and benzene are chosen as examples for continuous gas-phase processes, oxidation of pinene and propylene as examples for semi-continuous or batchwise processes in the liquid phase.


2021 ◽  
Author(s):  
Kaifeng Wang ◽  
Qiao Wu ◽  
Siwei Bi ◽  
Lingjun Liu ◽  
Guang Chen ◽  
...  

The gold(III)-catalyzed annulations of alkynes with anthranils were evaluated using DFT calculations. A unified rationale for the Br-migration on α-imino gold(III)-carbene was proposed, from which an unprecedented “N-donation/abstraction substitution” mechanism...


2013 ◽  
Vol 85 (8) ◽  
pp. 1671-1681 ◽  
Author(s):  
Mário M. Q. Simões ◽  
Cláudia M. B. Neves ◽  
Sónia M. G. Pires ◽  
M. Graça P. M. S. Neves ◽  
José A. S. Cavaleiro

Metalloporphyrins (MPs) are known to catalyze in vitro a broad range of cytochrome P450-mediated reactions occurring in vivo. Most of the biomimetic research using MPs in oxidative catalysis has been directed towards the oxidation of organic compounds presenting significant reactivity features in one functional group. Much less effort has been made to imitate the oxidation of more complex molecules, with a range of functionalities, such as drugs or other xenobiotics. By varying the structure of the porphyrin, the metal ion, the oxidant, and the reaction conditions, it is possible to modulate the regioselectivity of the oxidation reactions. Recently, and along with studies on the synthesis and reactivity of porphyrins, chlorins, and phthalocyanines, our group was able to develop an interesting line of research in the field of biomimetic oxidation of organic compounds using environmentally benign hydrogen peroxide as oxidant and Mn(III) or Fe(III) porphyrin complexes as catalysts. The more up to date results obtained in such work are reviewed here.


Sign in / Sign up

Export Citation Format

Share Document