Synthesis of Carbazoles by a Merged Visible Light Photoredox and Palladium-Catalyzed Process
作者:Sungkyu Choi、Tanmay Chatterjee、Won Joon Choi、Youngmin You、Eun Jin Cho
DOI:10.1021/acscatal.5b00817
日期:2015.8.7
Carbazoles have attracted great interest in recent years for a variety of applications in organic and medicinal chemistry as well as in materials science. In this work, an efficient method for the synthesis of carbazoles through the intramolecular C-H bond amination of N-substituted 2-amidobiaryls has been developed. Under visible light and an aerobic atmosphere, the transformation requires only catalytic amounts of Pd(OAc)(2) and [Ir(dFppy)(2)phen]PF6 (dFppy = 2-(2,4-difluorophenyl)pyridine; phen = 1,10-phenanthroline), the latter of which is utilized in synthetic chemistry for the first time. Spectroscopic and electrochemical studies revealed that the reaction is initiated by photoinduced electron transfer from a palladacyclic intermediate, formed from the 2-amidobiaryl and Pd-II species, to the photoexcited Ir catalyst. This step triggers reductive elimination in a Pd-III-containing palladacycle to produce the carbazole and a Pd-I species. The one-electron-reduced photocatalyst is reoxidized by O-2 to generate the original form of the photocatalyst, and the Pd-I species can be oxidized to the resting state through oxidative electron transfer to O-2 or the excited-state photocatalyst.
Intramolecular Oxidative C−N Bond Formation for the Synthesis of Carbazoles: Comparison of Reactivity between the Copper-Catalyzed and Metal-Free Conditions
作者:Seung Hwan Cho、Jungho Yoon、Sukbok Chang
DOI:10.1021/ja111652v
日期:2011.4.20
New synthetic procedures for intramolecular oxidative C-N bondformation have been developed for the preparation of carbazoles starting from N-substituted amidobiphenyls under either Cu-catalyzed or metal-freeconditions using hypervalent iodine(III) as an oxidant. Whereas iodobenzene diacetate or bis(trifluoroacetoxy)iodobenzene alone undergoes the reaction to provide carbazole products in moderate
已经开发了用于分子内氧化 CN 键形成的新合成程序,用于在 Cu 催化或无金属条件下使用高价碘 (III) 作为氧化剂从 N 取代的酰氨基联苯制备咔唑。虽然二乙酸碘苯或双(三氟乙酰氧基)碘苯单独进行反应以提供中低收率的咔唑产物,但三氟甲磺酸铜(II)和碘(III)物质的组合使用显着提高了反应效率,提供了更多样化的范围产品良率高。在包括动力学曲线、同位素效应和自由基抑制实验在内的机理研究的基础上,铜物种被提议用于催化激活高价碘 (III) 氧化剂。
Reported herein is an environmentally benign electrochemical C−H bond dehydrogenative amination protocol for the construction of privileged carbazole moiety with broad generality. Preliminary mechanistic investigations implied a radical reaction pathway. Compared with traditional ionic routes, the scalable transition‐metal and exogenous‐oxidant free strategy highlighted the green and sustainable nature