Nickel-mediated carboxylative cyclization of enynes

Nickel-mediated carboxylative cyclization of α,ω-enyne using carbon dioxide was investigated. Oxidative cycloaddition of enynes having an electron withdrawing group on alkene to a zero-valent nickel complex smoothly proceeded to provide nickelacyclopentene intermediates, which regioselectively reacted with CO₂ at the Csp³-nickel bond, giving cyclized carboxylation products in good yields.     

羧基化含氟聚芳醚的合成及涂层性能

以四烯丙基联苯二酚(TABP)、 双酚A和十氟联苯为原料, 通过室温缩聚制得含氟聚芳醚(FPAEs), 再将其与3-巯基丙酸进行加成, 制得羧基化含氟聚芳醚(CFPAEs). 通过改变TABP的投料量来调节产物的羧基含量. 以N-甲基吡咯烷酮(NMP)为溶剂, 将CFPAE涂层喷涂在马口铁上. 研究发现, CFPAE涂层具有优异的热稳定性和机械强度, 羧基的引入可显著提高含氟聚芳醚涂层的附着力. 当羧基含量为0.265 mmol/g时, 涂层的黏附力等级为0级, 铅笔硬度为6H, 不引起涂层破坏的最小轴棒直径为0.5 mm, 水接触角为103.9°. 此外, CFPAE涂层还具有优异的耐酸、 耐盐、 抗紫外老化和防腐蚀等性能. 研究结果表明, 羧基化是拓展含氟聚芳醚在特种氟碳涂料上应用的一种有效途径.     

Site-Selective Electrochemical C−H Carboxylation of Arenes with CO2

Herein, a direct, metal-free, and site-selective electrochemical C−H carboxylation of arenes by reductive activation using CO₂ as the economic and abundant carboxylic source was reported. The electrocarboxylation was carried out in an operationally simple manner with high chemo- and regioselectivity, setting the stage for the challenging site-selective C−H carboxylation of unactivated (hetero)arenes. The robust nature of the electrochemical strategy was reflected by a broad scope of substrates with excellent atom economy and unique selectivity. Notably, the direct and selective C−H carboxylation of various challenging arenes worked well in this approach, including electron-deficient naphthalenes, pyridines, simple phenyl derivatives, and substituted quinolines. The method benefits from being externally catalyst-free, metal-free and base-free, which makes it extremely attractive for potential applications.     

Butyl lithium (BuLi)-mediated carboxylation of vinylidenecyclopropanes with CO2

A novel butyl lithium (ⁿBuLi)-mediated carboxylation of vinylidenecyclopropanes with CO₂ in THF at −78 °C followed by the further transformation has been realized to afford the corresponding carboxylic adducts in moderate to good yields under normal conditions. The scope and limitations as well as the plausible reaction mechanism have been also discussed in this paper.     

Reductive carboxylation of aromatic esters by electron transfer from magnesium metal

Magnesium-promoted reductive carboxylation of ethyl benzoate in the presence of chlorotrimethylsilane in N,N-dimethylformamide brought about a new carbon-carbon bond formation between the carbonyl carbon atom and carbon dioxide to give the corresponding benzoylformic acid in good yield. It is noteworthy that only ethyl benzoates with substituents at the meta-position were converted into benzoylformic acid derivatives. Moreover, no mandelic acid was detected even under the reductive conditions. This result indicates that benzoylformic acid was obtained after hydrolysis of a carboxylated intermediate, which would be alive as a stabilized structure in the reaction media.     

Transition state structure invariance to model system size and calculation levels: a QM/MM study of the carboxylation step catalyzed by Rubisco

The present study elucidates structural features related to the molecular mechanism in the carboxylation step of the reaction catalyzed by Rubisco. Starting from the initial X-ray Protein Data Bank structure of a Rubisco monomer, the reactive subsystem in vacuo is subjected to quantum chemical semiempirical and ab initio studies, while the effects of the protein environments are included by means of a hybrid quantum mechanical/molecular mechanical (QM/MM) approach. The QM/MM is used to characterize the transition structure for carboxylation inside the protein. The calculations were made with the AM1/CHARMM/GRACE scheme. Comparisons between the in vacuo and in situ transition structures show remarkable invariance with respect to geometric parameters, index and transition vector amplitudes. The transition state couples the carbon dioxide attack to the C2 center of the substrate in its dienol form with a simultaneous intramolecular hydrogen transfer from the C2 atom to the hydroxyl group linked to the C3 center. This study suggests that carboxylation may be simultaneously coupled to the activation of the C3 center in the enzyme. Received: 24 March 1998 / Accepted: 3 September 1998 / Published online: 10 December 1998     

Oxidationsreaktionen am 1-(3,3-Dimethyl-5-norbornen-2-yl)ethanon und ein neuer Zugang zuendo-konfigurierten Isocamphanderivaten

The synthesis of some new compounds with the isocamphane skeleton obtained by oxidation reactions on the bicyclic ketone3 and its derivatives is described. Some possible routes to theendo-configurated camphenilanic acid (2) have been explored which yet have to be improved to furnish better yields. Separation of mixtures of the acids1 and2 failed. Carboxylation of camphenilone yielded only theexo-configurated isocamphenilanic acid (1).2, however, an important starting material for the preparation ofendo-configurated isocamphane derivatives, can be obtained easily with high yields and sterically pure by oxidation of camphene with H₂O₂/HCOOH. Thus a cheap, one-step method for the preparation of pure2 even in larger quantities is introduced.

Auszugsweise vorgetragen auf der 3. Wissenschaftlichen Tagung der Österreichischen Pharmazeutischen Gesellschaft am 18. Oktober 1982 in Innsbruck.     

Metalation/functionalization sequences applied to 2-bromo-3-fluoroquinolines

Mono- and disubstituted 2-bromo-3-fluoroquinolines 3 are readily accessible. They can be converted into the 3-fluoroquinoline-2-carboxylic acids 5 by consecutive halogen/metal permutation and into the 2-bromo-3-fluoroquinoline-4-carboxylic acids 6 by consecutive deprotonation and carboxylation. The latter compounds can be reduced to afford the 3-fluoroquinoline-4-carboxylic acids 7. The yields are excellent throughout. Rather than to introduce one functional group alternatively at the 2- or 4-position, one may also attach two different functional groups sequentially to both sites.     

Mechanism of the Ir/Pd catalyzed photocarboxylation of aryl halides

The recent Ir/Pd co-catalyzed photo carboxylation of aromatic halides with CO_2 has shown high efficiency and excellent functional group tolerance for preparing aromatic carboxylic acids and esters.With the aid of density functional theory(DFT) calculations,the carboxylation starts with two parallel steps,i.e.,oxidative addition of aromatic halides on Pd~0 and reductive quenching of the photocatalyst Ir(ppy)_2(dtbpy)~+with amine.Thereafter,a successive oxidation of Pd~Ⅱ with the amine radical(generated by the reaction of cationic radical amine and Cs_2 CO_3) and Ir~Ⅱ species occurs to generate Pd~0,from which the carboxylation occurs easily via a coordination,Pd-C insertion step.The release of the carboxylate product then regenerates the catalyst.