Arylboronic acids catalyzed

Certain pyrones react with active hydrogen compounds in a quite different way they display their alkenic character by participating in Michael reactions, thus coumarin itself gives 316 with malonate anion, and coumarins 317 react with arylboronic acids catalyzed by rhodium giving 318 in greater than 99% ee <2005OL2285>. 

Collman and Zhang276,296 proposed a mechanism for the coupling of imidazole with arylboronic acids catalyzed by [Cu(OH)-(tmeda)]2Cl2 (Scheme 13) that is similar to the... 

Hydroxymethylfurfural (HMF) can be formed from glucose and cellulose via an arylboronic acid-catalyzed dehydration in ionic liquid (13AJOC947). 

Mitsudo K, Shiraga T, Tanaka H (2008) Electrooxidative homo coupling of arylboronic acids catalyzed by electrogenerated cationic palladium catalysts. Tetrahedron Lett 49 6593-6595... 

Darses, S. Jeffery, T. Genet, J.P. Brayer, J.L. Demoute, J.P. (1996) Cross-coupling of arenediazonium tetrafluoroborates with arylboronic acids catalyzed by palladium. Tetrahedron Lett., 51, 3857-60. 

Microwave and fluorous technologies have been combined in the solution phase parallel synthesis of 3-aminoimidazo[l,2-a]pyridines and -pyrazines [63]. The three-component condensation of a perfluorooctane-sulfonyl (Rfs = CgFiy) substituted benzaldehyde by microwave irradiation in a single-mode instrument at 150 °C for 10 min in CH2CI2 - MeOH in the presence of Sc(OTf)3 gave the imidazo-annulated heterocycles that could be purified by fluorous solid phase extraction (Scheme 9). Subsequent Pd-catalyzed cross-coupling reactions of the fluorous sulfonates with arylboronic acids or thiols gave biaryls or aryl sulfides, respectively, albeit it in relatively low yields. 

Arylation of alkynes via addition of arylboronic acids to alkynes represents an attractive strategy in organic synthesis. The first addition of arylboronic acids to alkynes in aqueous media catalyzed by rhodium was reported by Hayashi et al.89 They found that rhodium catalysts associated with chelating bisphosphine ligands, such as 1,4-Ws(diphenyl-phosphino)butane (dppb) and 1,1 -/ E(diphenylphospliino)fcrroccnc... 

Rhodium-catalyzed Heck-type coupling of boronic acids with activated alkenes was carried out in an aqueous emulsion.82 The couplings between arylboronic acids and activated alkenes catalyzed by a water-soluble tm-butyl amphosrhodium complex were found to progress at room temperature to generate Heck-type products with high yields and excellent selectivity. It was necessary to add two equivalents of the... 

Generally, monophosphine complexes can be generated by decomposition of suitable precursors, among which the most notable are palladacycles (Section 9.6.3.4.7). A spectacular example makes use of spontaneous disproportionation of a dimeric complex of Pd1 with very bulky ligands to give one of the most reactive catalytic systems known so far, which catalyzes the fast crosscoupling of arylboronic acids with aryl chlorides and hindered aryl bromides at room temperature (Equation (28)) 389... 

So far, no systematic work has been done on the use of recyclable, solid-phase catalysts in cross-coupling reactions. Most of the examples have been obtained for cross-couplings with either arylboronic acids or terminal acetylenes. It should be noted, however, that due care should be exercised when interpreting results on the cross-coupling of arylboronic acids with aryl iodides, as this extremely facile reaction can be catalyzed by practically any palladium-containing material, including trivial Pd black,481 e.g., as a sediment on the reaction vessel. Therefore, this reaction cannot serve as a reliable test for comparison between different catalytic systems. 

Cationic palladium-catalyzed addition of arylboronic acids to nitriles for the formation... 

A parallel synthesis of a library of 2-aryl-6-chlorobenzothiazoles 112 involves a regioselective palladium-catalyzed Suzuki coupling reaction of 2,6-dichlorobenzothiazole 111 with arylboronic acids (1.1 equiv) under microwave irradiation <06TL3091>. When excess phenylboronic acid is used, Pd(PPh3)4 still provides 2-phenyl-6-chlorobenzothiazole exclusively, while 2-dicyclohexylphosphinobiphenyl 113 generates 2,6-diphenylbenzothiazole as the major product. 

A very recent addition to the already powerful spectrum of microwave Heck chemistry has been the development of a general procedure for carrying out oxidative Heck couplings, that is, the palladium)11)-catalyzed carbon-carbon coupling of arylboronic acids with alkenes using copper(II) acetate as a reoxidant [25], In a 2003 publication (Scheme 6.6), Larhed and coworkers utilized lithium acetate as a base and the polar and aprotic N,N-dimethylformamide as solvent. The coupling... 

The same research group additionally presented further investigations on fluor-ous-phase palladium-catalyzed carbon-carbon couplings [93]. Fluorinated aryl octyl-sulfonates were reacted in slight excess with arylboronic acids under microwave con-... 

Trost reported the synthesis of 1,4-dienes with ruthenium catalysis through regioselective carbometallation of alkynes with alkenes.51 Di- and trisubstituted olefins can also be obtained with arylboronic acids through an intermolecular process under rhodium,30 52 55 nickel,56 and palladium catalysis.57 Recently, Larock has reported an efficient palladium-catalyzed route for the preparation of tetrasubstituted olefins.58,59... 

Vinyl- or arylboronic acids also react with allenes, affording 1,3-dienes or styrene derivatives, respectively.89 This palladium-catalyzed addition proceeds with good regioselectivity and high stereoselectivity in favor of the formation of (ft)-trisubstituted isomer. 

Very recently, Murakami has published an Rh(i)-catalyzed cyclization of 1,6-enynes triggered by addition of arylboronic acids (Scheme 74).281 Initial carborhodation of the alkyne moiety is followed by insertion into the alkene moiety. /3-Alkoxy elimination provides the final product 289 in good yield and regenerates the catalyst species. 

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