Hydroarylation catalysis

Thanks to a recent renaissance in gold catalysis, new gold-mediated transformations are being discovered with ever-increasing frequency. Some of these discoveries have been attributed to the action of gold vinylidenes. Fiirstner and coworkers uncovered one such example while screening catalysts for intramolecular alkyne hydroarylation (Scheme 9.23) [46]. 

The scope and limitation of hydroarylation of acetylene carboxylic acid ester 4 using Au(I)-catalysis is revealed in Table 2. Electron-rich arenes participate well, but also furan and 2-methylfuran. p-Xylene leads to a 55 % yield, whereas an unacceptably low conversion results in the case of toluene. 

The Ru(II) catalysts currently used for olefin hydroarylation reactions are limited in terms of incorporation of substituents into the olefin substrate. For example, attempted hydrophenylation of isobutylene with TpRu(CO)(NCMe)(Ph) as catalyst does not yield new organic products. In addition, extension of catalysis to hetero-functionalized olefins using the TpRu(CO)(NCMe)(aryl) systems has not been successful. For electron-deficient olefins (e.g. styrene, methyl methacrylate, acrylonitrile) the TpRu(II) complexes initiate radical polymerization of the olefin in transformations that probably involve a Ru(III/II) redox change [4]. The... 

Under palladium catalysis, a,/3-unsaturated ketones can undergo Michael-type Heck hydroarylationsJ Recently, the intermolecular hydroarylation of 19 has been realized in supercritical carbon dioxide as a solvent to furnish the products 21 (Scheme Triethylamine is believed to be the source of hydride in these transformations. With certain combinations of substituents R R on the enone 19 and the aryl iodide, significant fractions of the /3-dehydropalladation products 22 were also formed, and the aryl-substituted unsaturated 22 was the sole product when acrylates 19 (R = OEt) were subjected to these conditions. The highly di-diastereoselective hydroarylation of an a,/3-unsaturated ketone 23 (Scheme has been applied in an intramolecular fashion toward the synthesis of the octahydrophenanthrene derivative 24, a novel biomarker from Brazilian marine evaporitic Carmopolis oil. 

The intramolecular reaction between furans and alkynes often does not yield the expected hydroarylation products, but, instead, gives phenols 6.220 in an efficient and selective manner (Scheme 6.96). This reaction was probably the first surprising transformation from gold catalysis, indicating that gold could be more than just an electrophilic trigger. 

In 2009, a wide range of optically active chromans and tetrahydroquinolines were synthesised by Xiao et al. on the basis of the first enantioselective organo-catalytic intramolecular hydroarylations of phenol- and aniline-derived enals. Good yields combined with good to high enantioselectivities of up to 96% ee were obtained for the Michael adducts generated by catalysis with a diarylprolinol silyl ether (Scheme 1.83). 

To date, most research on NHCP transition-metal catalysis has been devoted to cross-couplings [13] or related reactions such as hydroarylation of alkenes [18], direct arylation of alkynes [17], or oxidative homocoupling of terminal alkynes [19]. All NHCP systems used in these studies feature one or two... 

Scheme 7.67 Tandem hydroamination-hydroarylation-transfer hydrogenation reaction catalysed by gold catalysis and chiral phosphoric acid...

Keywords Alkene hydroarylation Alkenylation Alkylation Alkyne hydroarylation Annulations Arylation C-C bond cross-couplings Heteroaiylation Ruthenmm(ll) catalysis sp C-H bond activation... 

By combining an initial gold-catalyzed hydroaminative indole formation with repetitive hydroarylations, Hirano et al. [48] reported the gold-catalyzed direct construction of highly fused carbazoles by multiple cyclization. Scheme 4.28 shows one example of this chemistry, and the overall yield of this pentacyclization is excellent, highlighting the efficiency of gold catalysis. 

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