Cross aryl ether bond

Figure 9.44 Lignin compounds, composed of connecting units of monolignols cross linked by carbon to carbon and the dominant /3-0-4 aryl to aryl ether bonds.

Nickel-catalyzed cross-couplings of aryl ether bonds is well documented [49,50]. A recent example has demonstrated a convenient route for the synthesis of a ter-aryl [51]. 

In addition to /3-H elimination, olefin insertion, and protonolysis, the cr-metal intermediate has also proved to be capable of undergoing a reductive elimination to bring about an alkylative alkoxylation. Under Pd catalysis, the reaction of 4-alkenols with aryl halides affords aryl-substituted THF rings instead of the aryl ethers that would be produced by a simple cross-coupling mechanism (Equation (126)).452 It has been suggested that G-O bond formation occurs in this case by yy/z-insertion of a coordinated alcohol rather than anti-attack onto a 7r-alkene complex.453... 

Collman and Zhong reported the first catalytic, oxidative C-N cross coupling between an arylboronic acid and a substrate containing an N-H bond. " In the presence of 10 mol % of commercially available [Cu(OH)TMEDA]jClj in dichloromethane, imidazole coupled with phenylboronic acid at room temperature. Lam and co-workers and Antilla and Buchwald expanded the scope of this type of catalytic coupling to encompass the reactions of amines. Lam and co-workers reported the first catalytic version of the reactions of aiylboronic acids with phenols to yield aryl ethers in good yields. The highest yields were obtained when Oj was used as co-oxidant. After these early discoveries, several reports on... 

Hardwood lignins present in their structure both guaiacyl- and syringyl-propane units. Lignin contains mainly glycerol-aryl ether hnkages, but there are also present various types of C-C bonds which may act as cross-linkages between relative short, linear chains of phenyl-propane units. 

As described in the previous section, Ni(0)/PCy3 is an effective catalyst system for cross-coupling using conventionally inert phenolic electrophiles, including aryl ethers, carboxylates, and carbamates. In this section, the C-O bond activatimi reactions catalyzed by other metals are described. 

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

Cross-coupling reactions 5-alkenylboron boron compounds, 9, 208 with alkenylpalladium(II) complexes, 8, 280 5-alkylboron boron, 9, 206 in alkyne C-H activations, 10, 157 5-alkynylboron compounds, 9, 212 5-allylboron compounds, 9, 212 allystannanes, 3, 840 for aryl and alkenyl ethers via copper catalysts, 10, 650 via palladium catalysts, 10, 654 5-arylboron boron compounds, 9, 208 with bis(alkoxide)titanium alkyne complexes, 4, 276 carbonyls and imines, 11, 66 in catalytic C-F activation, 1, 737, 1, 748 for C-C bond formation Cadiot-Chodkiewicz reaction, 11, 19 Hiyama reaction, 11, 23 Kumada-Tamao-Corriu reaction, 11, 20 via Migita-Kosugi-Stille reaction, 11, 12 Negishi coupling, 11, 27 overview, 11, 1-37 via Suzuki-Miyaura reaction, 11, 2 terminal alkyne reactions, 11, 15 for C-H activation, 10, 116-117 for C-N bonds via amination, 10, 706 diborons, 9, 167... 

Cross-coupling reactions leading to the formation of C-X (X = heteroatom) bonds catalyzed by Pd(dba)2 have been reported. Aniline derivatives have been prepared via reaction of amine nucleophiles with aryl halides in the presence of Pd(dba)2 and phosphines, especially P( Bu)3. Likewise, diaryl and aryl alkyl ethers are produced from aryl halides (Cl, Br, I) and sodium aryloxides and alkoxides under similar conditions. Conditions effective for the coupling of aryl chlorides with amines, boronic acids, and ketone enolates using an easily prepared phosphine chloride as a ligand have recently been uncovered (eq 22). The preparation of aryl siloxanes and allyl boronates via Pd(dba)2-catalyzed C-Si and C-B coupling have been reported as well. 

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