substitution even in the presence of strong electron‐donating groups and enables de‐tert‐butylation required for the complete annulation. Also demonstrated is the applicability of the method to introduce five‐, six‐, and seven‐membered rings containing oxygen, whereas multiple annulations also open up a short synthetic path to ladder‐type O‐heteroacenes and oligodibenzofurans.
Nickel(0)/Imidazolium Carbene Catalyst System for Efficient Cross-Coupling of Aryl Bromides and Chlorides with Organomanganese Reagents
作者:Anne Leleu、Yves Fort、Raphaël Schneider
DOI:10.1002/adsc.200505409
日期:2006.6
6-diisopropylphenyl)imidazolium chloride associated with nickel(II) acetylacetonate (3–5 mol %) was used as catalyst to efficiently cross-couple functionalized arylbromides with organomanganese reagents. The reactions were performed between 0 °C and room temperature, giving unsymmetrical biaryls in 0.25 to 24 h with 52 to 100 % yields for isolated materials. Arylchlorides showed slightly diminished reactivity
A new strategy for the synthesis of 2‐aryl‐ and 2‐heteroaryl fluoroarenes has been developed. An intermolecular domino Grignard‐coupling–fluorination sequence affords a range of 2‐fluorobiaryls from aryl bromides under mild conditions. This methodology can be further extended to the synthesis of 2′‐aryl‐2‐fluorobiphenyls.
A mild robust generic protocol for the Suzuki reaction using an air stable catalyst
作者:Jonathan D. Moseley、Paul M. Murray、Edward R. Turp、Simon N.G. Tyler、Ross T. Burn
DOI:10.1016/j.tet.2012.05.030
日期:2012.7
A mild but robust procedure has been developed as a first pass generic protocol for the Suzuki-Miyaura reaction. The protocol employs an air stable palladium pre-catalyst at low loading (<= 1 mol %) in aqueous solvent mixtures at moderate temperature using potassium carbonate as base. Under these mild conditions, most aryl bromides will react with sterically and electronically demanding aryl boronic acids to give complete conversion to the product biphenyls in less than 1 h. Aryl chlorides are also fully converted in most cases either under identical conditions in 8-24 h, or in 2 h at elevated temperature. A further advantage of these mild conditions of moderate temperature, weak base and benign solvent is that sensitive functional groups and structural motifs are well tolerated. In addition, the lipophilic biphenyl products are readily isolated after a simple work-up procedure. These generic conditions are ideal for proof of transformation, and as the starting point for development and optimization of a specific process. The discovery and fine-tuning of this generic protocol will be presented, supported extensively by examples to illustrate its scope and utility. (C) 2012 Elsevier Ltd. All rights reserved.
Activation of reducing agents. Sodium hydride containing complex reducing agents. 32. NiCRAL's as very efficient agents in promoting cross-coupling of aryl halides