Organic halides biaryl preparation

The palladium-catalysed Suzuki coupling reaction of aryl halides with arylboronic acids has proved to be a general and convenient synthetic tool employed in organic chemistry to prepare biaryl compounds.[1] The discovery and development of active and efficient palladium-catalyst systems have been the focus of great interest recently. New catalytic systems based on paUadium-oxazolines, such as 2-aryl oxazolines and 2,2 -(l,3-phenylene)bisoxazoline (Figure 4.1) have been developed for the coupling reaction. These catalytic systems have the potential to overcome... 

Biaryl structures are found in a wide range of important compounds, including natural products and organic functional materials [8,80,81]. One of the most common and useful methods for preparing biaryls is the palladium-catalyzed coupling of aryl halides with arylmetals (Scheme 1, mechanism A). On the other hand, aryl halides have been known to couple directly with aromatic compounds as formal nucleophiles under palladium catalysis. While the intramolecular cases are particularly effective, certain functionalized aromatic compounds such as phenols and aromatic carbonyl compounds, as well as... 

The reaction of 1,3-dinitrobenzenes with aryl iodides can be accomplished by using copper(I) tert-butoxide in situ prepared from CuCl and potassium rert-butoxide in dry DME. In this case, the reaction can be realized under essentially milder reaction conditions, at 70-110 C in the presence of pyridine as the base with respective yields. For instance, the biaryl 40 was produced from compounds 38 and 39 after 20 h at 67 C in DME / pyridine as the reaction solvent in 95% yield, respectively [38]. Dehalogenation products were isolated from many Ullmann reactions performed with the (relatively acidic) nitro-aryl halides, even when exclusion of water or acidic (protic) substances was provided. Furthermore, nitro-aryl halides are partially converted to triarylamines by reduction and subsequent exhaustive A -arylation [44,45]. Finnaly, it can be concluded that the Ullmann and related reactions are still valuable tools in the preparative organic chemistry providing a simple and usually efficient approach to simple symmetrical and certain classes of unsymmetrical biaryls. 

Many reviews have been published in the last few years on the applications of the Hiyama cross-coupling reaction in organic synthesis. In general, preparation of biaryls or heterobiaryls is the most common application of this reaction since new methodology development is based on examples of these. The most prevalent applications of the aryl and heteroaryl halides with organosilane precursors involve reactions such as vinylations, alkenylations, and alkynylations. The reader is encouraged to consult these key reviews. This section will describe some of the more recent applications published in the last few years. 

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