Cobalt-catalyzed arylations

Fig. 70 Electrochemically mediated cobalt-catalyzed aryl radical 5-exo cyclizations...

Cobalt-catalyzed Aryl Radical Cyclizations with Grignard Reagent... 

Copper- and Cobalt-Catalyzed Arylations of Alkyl (Pseudo]Halides... 

Yoshikai and Gao reported on the cobalt-catalyzed arylation of aldimines using a directed C—H bond functionalization. A series of 2-arylpyridines were treated with A-phenylbenzaldimine in the presence of CoBr2, IPrHCl, and t-BuCH2MgBr followed by an acid workup to give the desired ortho addition products 215-217 in good yield. 

CHROMIUM TRIOXIDE-PYRIDINE COMPLEX, preparation in situ, 55, 84 Chrysene, 58,15, 16 fzans-Cinnamaldehyde, 57, 85 Cinnamaldehyde dimethylacetal, 57, 84 Cinnamyl alcohol, 56,105 58, 9 2-Cinnamylthio-2-thiazoline, 56, 82 Citric acid, 58,43 Citronellal, 58, 107, 112 Cleavage of methyl ethers with iodotri-methylsilane, 59, 35 Cobalt(II) acetylacetonate, 57, 13 Conjugate addition of aryl aldehydes, 59, 53 Copper (I) bromide, 58, 52, 54, 56 59,123 COPPER CATALYZED ARYLATION OF /3-DlCARBONYL COMPOUNDS, 58, 52 Copper (I) chloride, 57, 34 Copper (II) chloride, 56, 10 Copper(I) iodide, 55, 105, 123, 124 Copper(I) oxide, 59, 206 Copper(ll) oxide, 56, 10 Copper salts of carboxylic acids, 59, 127 Copper(l) thiophenoxide, 55, 123 59, 210 Copper(l) trifluoromethanesulfonate, 59, 202... 

A cobalt-catalyzed method for arylation of heteroarenes including thiazole and benzothiazole was reported in 2003 <030L3607>. According to this report, the direct C-5 arylation of thiazole with iodobenzene was carried out in the presence of cobalt catalyst [Co(OAc)2/IMes] and cesium carbonate, and a complete reversal of arylation from C-5 to C-2 was observed with the bimetallic Co/Cu/IMes system. This report has been retracted as the laboratory of the senior author has not been able to reproduce the key results disclosed in the communication <06OL2899>. 

Aryl-4,5-dihydrooxazoles 556 underwent cobalt-catalyzed carbonylation to give 4,5-dihydro-l,3-oxazin-6-ones 557, usually in good yields, but an exception was the ring enlargement of 556 containing a 5-methyl (R = Me) or a sterically bulky 2-(o-tolyl) substituent (Equation 67) <20030L1575>. 

Since Wakamatsu serendipitously discovered amidocarbonylation while performing the cobalt-catalyzed hydroformyla-tion of olefins in 1971, this unique carbonylation reaction, affording a-amino acids directly from aldehydes, has been extensively studied.More recently, palladium-catalyzed processes have been developed to expand the scope of this reaction.The Pd-catalyzed amidocarbonylation has been applied to aldehydes,aryl halides, and imines. As a related reaction, lactamization " of aryl halides catalyzed by a rhodium complex has also been developed. 

Aryl-4,5-dihydrooxazoles 380 undergo cobalt-catalyzed carbonylation to give 4,5-dihydro-l,3-oxazin-6-ones 381, generally in good yields (Scheme 177) <20030L1575>. 

Kom, T. J., Cahiez, G., Knochel, P. New cobalt-catalyzed cross-coupling reactions of heterocyclic chlorides with aryl and heteroaryl magnesium halides. Syn/etf 2003,1892-1894. 

Other C-C bond-forming reactions have been successfully developed using SCCO2 and liquid CO2 as reaction media. Examples include the synthesis of cyclopentenones via cobalt-catalyzed cocyclizations of alkynes with alkenes and carbon monoxide (Pauson-Khand reaction) (Scheme 30) , enantioselective nickel-catalyzed hydrovinylation of styrenes (Scheme 31) , and the palladium-catalyzed hydroarylation of acyclic jS-substimted-o , j8-enones with aryl iodides (formal conjugate addition) (Scheme 32). ... 

Facile insertion of CO takes place, and the reaction offers a synthetic method of orf/to-substituted benzoic acid derivatives. The 2-aryl-3-indazolone 421 was obtained in high yield by carbonylation of 4-methylazobenzene complex 420 in alcohol or water [176]. Cobalt-catalyzed carbonylation of 421 and subsequent hydrolysis afforded aniline and 5-methylanthranilic acid (422). The results show that the cr-bond formation is an electrophilic substitution of PdCl2 on the benzene ring [176,177]. 

Although cobalt catalysis is somewhat less developed compared to other transition metal catalysis for cross-coupUngs, but has shown rather unconventional, novel reactivity profiles [50]. For example, Oshima reported a cobalt-catalyzed tandem radical cyclization/cross-coupling reaction between an aryl Grignard reagent and an alkyl halide bearing an (o-alkenyl group (Equation 5.44) [51]. 

Highly stereoselective arylation reactions were reported, as shown in Equation 5.46. With an optically active diamine ligand, a modest asymmetric induction was observed (Equation 5.47). An asymmetric synthesis of a synthetic prostaglandin AH 13 205 was accomplished using the diastereoselective cobalt-catalyzed cycliza-tion/arylation sequence as key step [55]. 

Table 5.5 Cobalt-catalyzed cross-coupling (and tandem cyclization/arylation) reactions between unactIvated alkyl halides and aryl metal reagents.

In 1990 Alper and Lee reported on a cobalt-catalyzed carbonylation of aryl iodides and alkyl iodides [293, 294]. In the presence of cobalt chloride or acetate, potassium cyanide, base, and PEG-400, carboxylic acids were produced from the corresponding iodo compounds. Lewis acids, such as boron trifluoride etherate... 

Chiral l-aryl-5,6,7,8-tetrahydroquinolines (136) were synthesized by photo induced chiral cobalt-catalyzed [2-1-2-1-2] cycloaddition reaction of l-aryl-l,7-octadiynes (134) and nitriles (135). ... 

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