Aryltrifluoroborate, arylation with

The formation of an aryl-O bond by the reaction of a phenol with air and moisture stable potassium alkenyl and aryltrifluoroborates was mediated by a copper species. The reaction procedure involved catalytic amounts of Cu(OAc)2 with DMAP as a ligand in the presence of oxygen and molecular sieves. A variety of aliphatic primary and secondary alcohols as well as phenols were suitable reaction partners, thus displaying a broad functional group tolerance (Equation (237)).1025... 

The Pd-catalysed Miyaura-Suzuki coupling of aryltrifluoroborates with 4-tosyloxycoumarins in aqueous conditions offers an attractive route to 4-arylcoumarins <06TL1525> and 4-hydroxycoumarins have been converted into a mixture of predominantly thiopyrano[5, 4 3,4]- pyrano[5,6-c]coumarins and [6,5-c]chromones in a one-pot tandem Knoevenagel - HDA sequence with an S-prenylated 1-phenyl-lff-pyrazole-4-carbaldehyde <06TL2265>. The benzopyrano[4,3-c]benzopyranone system can be obtained from 3-aryl-4-methylcoumarins by deprotonation of the methyl function and subsequent elaboration <06TL5909>. 

In a related reaction, aryltrifluoroborates PhBF3 X (12-28), are coupled to aryl halides with a palladium catalyst to give the biaryl. ... 

Recently, Zhang and coworkers reported a direct palladium-catalyzed C-2 arylation of indoles with potassium aryltrifluoroborate salts [204]. Remarkably, the direct arylation took place at room temperature when acetic acid was used as the solvent. 

The advantage of this method was the low cattilyst loading involved. In fact, just 0.25 mol% of rhodium dimer catalyst afforded the expected benzophenone with full conversion (see Scheme 7.16). So, a straightforward synthetically useful route to congested benzophenone frameworks starting from readily available aryl aldehydes and potassium aryltrifluoroborates was described. Neutral conditions allow the direct formation of di-, tri-, and even tetra-orf/ro-substituted benzophenones under operationally simple conditions in very good yields, thanks to the use of a stable phosphonium salt of P(fBu)3. 

In a later study, Zhao reported the arylation of indolizines with aryltrifluoroborate salts and used this same Pd(OAc)2/AgOAc catalyst system to affect C3-alkynylation with phenylpropiolic acids via a decarboxylative pathway. ... 

The decarboxylative arylation of potassium oxalate monoesters also occurs to give the corresponding aromatic esters (Scheme 4.68) [70]. The decarboxylative oxidative coupling of a-keto carboxylic acids with aryltrifluoroborates takes place in the presence of a palladium catalyst together with (NH4)2S20g as oxidant (Scheme 4.69) [71]. a-lmino carboxylates also undergo decarboxylative... 

The reaction was also extended to aliphatic alcohols. In this case more reactive aryltrifluoroborates had to be used instead of boronic acids to give good to excellent yields of arylalkyl ethers. As with amination, successful results were obtained with Cu(OAc)2 immobilized on a solid support. A-Substituted hydroxylamines were also employed as substrates in the oxidative 0-arylation. Thus A-hydroxyphthalimide was treated with excess arylboronic acids in presence of Cu(OAc)2, base, and molecular sieves to give 0-aryloxyamines in good to excellent yields (eq 25). ... 

Potassium aryltrifluoroborate salts are excellent coupling partners for free or protected NH-indoles at the C-2 position the palladium- and copper-catalyzed transformation takes place under mild conditions, in air, at room temperature. Furthermore, conditions were developed for the coupling of indoles with aryl boronic acids, employing Pd(OAc)2 as the catalyst and a copper salt or O2 as the oxidant. ... 

Direct Arylation ofindolizines with Aryltrifluoroborate Salts. 

Another approach to the conversion of aryltrifluoroborate salts into aryl fluorides also used a common copper salt to promote the reactions however, this chemistry used an electrophilic source of fluorine (Scheme 7.58) [84]. The most effective source of F was found to be A-fluoro-2,4,6-trimethylpyridinium ttiflate. Similar to the authors previous work with arylstannanes, the key to the synthesis was prestirring the F source and the copper complex prior to the introduction of the aryltrifluoroborate salts. Using this system, a wide range of aryltrifluoroborate salts bearing ethers, halogens, aldehydes, ketones, amides, and esters were converted into aryl fluorides. 

---