and heterocyclic arenes with aryl iodides, bromides, and chlorides has been developed. These reactions occur in excellent yield and are highly selective. Studies with aryl iodides substrates revealed that catalyst poisoning occurs due to the accumulation of iodide in the reaction media. This can be overcome by the addition of silver salts which also permits these reactions to occur at lower temperature
已开发出一种用于将多种简单和杂环芳烃与芳基碘化物、溴化物和氯化物进行分子内直接芳基化的催化剂。这些反应以极好的收率发生并且具有高度选择性。对芳基碘化物底物的研究表明,由于碘化物在反应介质中的积累,会发生催化剂中毒。这可以通过添加银盐来克服,银盐也允许这些反应在较低温度下发生。该方法的效用通过咔唑天然产物的快速合成和通过直接芳基化产物的开环反应合成空间位阻四邻位取代的联芳基来说明。机理研究提供了对催化剂的深入了解 s 作用模式并显示在钯催化的简单芳烃的直接芳基化中存在动力学上显着的 CH 键裂解。从这些研究中获得的知识导致了以前无法获得的芳烃的新分子间芳基化反应的发展,为其他新的直接芳基化过程的发展打开了大门。
Direct Transition-Metal-Free Intramolecular Arylation of Phenols
作者:Gan B. Bajracharya、Olafs Daugulis
DOI:10.1021/ol801897m
日期:2008.10.16
base-mediated intramolecular arylation of phenols with aryl halides has been developed. In the presence of 2.5 equiv of t-BuOK in dioxane at 140 degrees C, the intramolecular cyclization of 3-(2-halobenzyloxy)phenols affords 6H-benzo[c]chromenes in high yields. This reaction proceeds by an initial formation of a benzyne intermediate followed by an aromaticsp(2) C-H functionalization (a formal C-H activation)
In this Communication, we describe direct arylation reactions with improved scope and catalyst activity for the intramolecular formation of biaryl compounds. This was achieved through the establishment of a highly active and robust catalyst system and the subsequent development of a novel phosphine ligand 27. The enhanced catalytic activity extends these transformations to include previously unreactive and poorly reactive substrates, and allows for very low catalyst loadings to be employed-as little as 0.1 mol %.
Mild and efficient palladium-catalyzed intramolecular direct arylation reactions
作者:Marc Lafrance、David Lapointe、Keith Fagnou
DOI:10.1016/j.tet.2008.01.057
日期:2008.6
been evaluated in the context of intramoleculardirect arylation reactions. Under the optimal conditions, arylation of simple arenes can be performed under very mild conditions, with heating to 50 °C. The role of the pivalic acid additive is rationalized by invoking a concerted palladation–deprotonation pathway where the pivalate is behaving as either an intramolecular base from the palladium metal or
Bu3SnH mediated oxidative radical cyclisations: synthesis of 6H-benzo[c]chromen-6-ones †
作者:W. Russell Bowman、Emma Mann、Jonathan Parr
DOI:10.1039/b002539i
日期:——
Attempts to synthesise 6H-benzo[c]chromen-6-ones by Bu3SnH mediated cyclisation of o-(benzoyl)aryl radicals failed because of the preferred trans conformation of the ester. This problem was overcome by using cyclisation of o-(benzyloxy)aryl and o-[(aryloxy)methyl]aryl radicals to yield 6H-benzo[c]chromenes followed by oxidation to the 6H-benzo[c]chromen-6-ones. 3-Methoxy-6H-benzo[c]chromen-6-one 1, one of the main biologically active constituents of shilajit, a herbal medicine used in countries surrounding the Himalayan mountains, was synthesised using Bu3SnH mediated cyclisation of 1-benzyloxy-2,4-dibromo-5-methoxybenzene 31 to yield 3-methoxy-6H-benzo[c]chromene 25 followed by PCC oxidation of the 6-position. In order to avoid the problems of rearrangement, the aryl radical cyclisation must be designed such that whichever way the spirodienyl intermediate rearranges, the same product is obtained. For instance, the Bu3SnH mediated cyclisation of 1-iodo- and 1-bromo-2-(3-methoxyphenyloxymethyl)benzenes 22 and 23 respectively gave both the isomers, 1-methoxy-6H-benzo[c]chromenes 24 and 3-methoxy-6H-benzo[c]chromenes 25via rearrangement of the intermediate spirodienyl radical. The synthesised 6H-benzo[c]chromenes were oxidised in high yield to the corresponding 6H-benzo[c]chromen-6-ones. The mechanism of the ‘oxidative’ Bu3SnH mediated cyclisation is discussed.