Biaryls, preparation

Biaryls, preparation by Pd-catalyzed aryl-aryl coupling, 66, 73 Bicyclo[2.2.1 Jhepta-2,5-diene-1,4-bis(diphenylphosphino)butanerhodium trifluoromethanesulfonate, 68, 64... 

Keywords Arenes, polycyclic, biaryls, preparation, review. 

Regioselective C-H activation is often used for intramolecular biaryl preparations in Pd-mediated transformations. Thus concise syntheses of a large collection of alkaloids have been reported using variations of this approach (239-241), which differ mainly in terms of the functionalization of the precursor, palladium catalysts, and ligands. An efficient synthesis of racemic y-lycorane was recently disclosed whereby the key step is the intramolecular a-arylation of a cyclohexanone derivative (242). Some heterocycKc synthetic precursors (e.g. substituted indoles, quinolines, quinolones, phenanthridines, and phenanthridinones) have also been prepared en route to the alkaloids [hippadine, trisphaeridine (70), and crin-asiadine] via Pd- and Cu-mediated reactions (243,244). 

The Ullmann synthesis of unsymmetrical biaryls Preparation of l-(2-methoxycarbonyl-4-nitrophenyl)-4-nitronaphthalene (30) [38]... 

The Cohen s method for performing the Gatterman synthesis of symmetrical biaryls Preparation of 4,4 -dinitrobiphenyl (61) [94]... 

Palladium-based methods for coupling of aryl halides always require more drastic reaction conditions than nickel based methods because of lower reactivity of palladium-complexes in the same reactions. However, Pd(PPh3)4, in situ formed by electrochemical reduction of mixture of Pd(PPh3)2Cl2 and PPh3, catalyses the crosscoupling of two different aryl iodides with similar selectivity, but at room temperature [10]. Unsymmetrical biaryls prepared by any of these methods were usually purified... 

The Motherwell synthesis of biaryls Preparation of 2N-methyl-4%6-dimethyl-I-aminobiphenyl (537) I4j... 

The Meyers synthesis of biaryls Preparation of biphenyl-2-carboxylic acid (543) [40)... 

Enantioselective Hayashi synthesis of biaryls Preparation of (R)-2,2 -dimethyl-l,V-binaphthyl (630) [34]... 

With the polyamidourea dendrons the increase in loading was even more dramatic (up to 230 nmol/bead). The high per-bead loading of the terminal functional groups enabled the analysis of compounds cleaved from a single bead for these dendrons (e.g., biaryls prepared on the resin were analyzed by HPLC and NMR). 

The UUmann synthesis of symmetrical biaryls Preparation of 2,2 -dimethoxy-4,4 -dimetho3 carbonyibiphenyl (64) [15]... 

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