为了证明异氰化物在催化CH键官能化反应中的实用性,开发了2-卤代双芳基与异氰化物的钯催化的环偶联反应。该反应通过在2-卤代联芳基的2'-位上的CH键断裂,提供了一系列芴酮亚胺衍生物。2,6-二取代的苯基异氰化物的使用对于进行该催化环偶联反应至关重要。该反应适用于杂环和乙烯基底物,从而允许构建广泛的环系统。观察到的大的动力学同位素效应(k H / k D = 5.3)表明,CH键的活化是该催化作用中的周转限制步骤。
Examination of the Mechanism of Rh2(II)-Catalyzed Carbazole Formation Using Intramolecular Competition Experiments
摘要:
The use of a rhodium(II) carboxylate catalyst enables the mild and stereoselective formation of carbazoles from biaryl azides. Intramolecular competition experiments of triaryl azides suggested the source of the selectivity. A primary intramolecular kinetic isotope effect was not observed, and correlation of the product ratios with Hammett sigma(+) values produced a plot with two intersecting lines with opposite rho values. These data suggest that electronic donation by the biaryl pi-system accelerates the formation of rhodium nitrenoid and that C-N bond formation occurs through a 4 pi-electron-5-atom electrocyclization.
carbonylation reaction for the synthesis of fluoren‐9‐ones from 2‐halogenated biphenyls using phenyl formate as a carbon monoxide surrogate was achieved. The combined use of cesium carbonate and o‐anisic acid resulted in a remarkable rate enhancement, where the reaction was complete within 3 min in some cases. Mechanistic studies indicated that the turnover‐limiting step of the reaction was the C−H bond‐cleaving
2-halobiaryls with isocyanides was developed. The reaction afforded an array of fluorenone imine derivatives via the cleavage of a C−H bond at the 2′-position of 2-halobiaryls. The use of 2,6-disubstitutedphenyl isocyanide was crucial for this catalytic cyclocoupling reaction to proceed. The reaction was applicable to heterocyclic and vinylic substrates, allowing the construction of a wide range of
为了证明异氰化物在催化CH键官能化反应中的实用性,开发了2-卤代双芳基与异氰化物的钯催化的环偶联反应。该反应通过在2-卤代联芳基的2'-位上的CH键断裂,提供了一系列芴酮亚胺衍生物。2,6-二取代的苯基异氰化物的使用对于进行该催化环偶联反应至关重要。该反应适用于杂环和乙烯基底物,从而允许构建广泛的环系统。观察到的大的动力学同位素效应(k H / k D = 5.3)表明,CH键的活化是该催化作用中的周转限制步骤。
Examination of the Mechanism of Rh<sub>2</sub>(II)-Catalyzed Carbazole Formation Using Intramolecular Competition Experiments
作者:Benjamin J. Stokes、Kathleen J. Richert、Tom G. Driver
DOI:10.1021/jo901224k
日期:2009.9.4
The use of a rhodium(II) carboxylate catalyst enables the mild and stereoselective formation of carbazoles from biaryl azides. Intramolecular competition experiments of triaryl azides suggested the source of the selectivity. A primary intramolecular kinetic isotope effect was not observed, and correlation of the product ratios with Hammett sigma(+) values produced a plot with two intersecting lines with opposite rho values. These data suggest that electronic donation by the biaryl pi-system accelerates the formation of rhodium nitrenoid and that C-N bond formation occurs through a 4 pi-electron-5-atom electrocyclization.