Coupling Reactions of Aryl Fluorides

As above described, Bu-P4 base was found to catalyse the coupling reaction of aryl fluorides with silyl ethers. The use of silyl ether was required for these reactions, and direct arylation of unsilylated alcohols using superbase catalysed coupling reactions has been a challenge. Therefore, the combination of triethylsilyl hydride (Et3SiH) and catalytic Bu-P4 is considered to represent an attractive hydride generating system with which to carry out sequential deprotonation and Sj-jAr reaction [55] (Figure 5.5). 

For other examples of palladium-catalyzed coupling reactions of aryl fluorides, see (a) Mikami, K.,... 

Allyl carbonates (Schemes 17 and 18) and diene monoxides (Scheme 19) were also employed in the Pd-catalyzed coupling reaction of aryl- and alkenylsilanes.t t The reaction does not require activation by a fluoride ion or an additional base like a hydroxide ion. 

Trifluoromethylalion of aryl iodides was carried out by the fluoride ion in duced cross-coupling reaction of aromatic iodides with tnfluoromethyltnalkyl-silanes in the presence ofcopper(I) salts [219 (equation 147) Some pentafluoro- ethyl derivative was also formed This methodology was extended to pentafluoroethyl-and heptafluoropropyltriethylsilanes [2/9]... 

The arylation of heteroaromatic compounds is also achieved by aryl-aryl coupling reaction. The arylation of A-methylimidazole with bromobenzene occurs under palladium catalysis (Equation (62)).72 The arylation of thiazole with aryl iodide occurs at the 2-position under PdCl2(PPh3)2/CuI catalysis.73 In this case, tetrabutylammonium fluoride improves the activity of the catalyst. Alternatively, thiazoles and benzothiazole are efficiently arylated... 

Lithiation of compound 560 with s-BuLi-TMEDA in THF at —78 °C following an inverse addition protocol provided the anion 561. It reacts with primary alkyl iodides and triflates, silyl chlorides, diphenyl disulfide, epoxides, aldehydes, ketones, imines, acyl chlorides, isocyanates and sulfonyl fluorides to yield the expected compounds 562 (Scheme 152). The transmetallation of compound 561 with ZnBr2 allowed the palladium-catalyzed cross-coupling reaction with aryl and vinyl bromides837. When the reaction was quenched with 1,2-dibromotetrafluoroethane, the corresponding bromide 562 (X = Br) is obtained838. 

The coupling reaction of arylsilanes with aryl iodides is also mediated by a palladium catalyst and a fluoride ion [23,24]. Optimized reaction conditions are as... 

Under an atmospheric pressure of carbon monoxide, aryl- and alkenylsilanes undergo a carbonylative coupling reaction with aryl and alkenyl halides [44,45]. The optimized conditions for arylsilanes involve the use of N,M-dimethyl-2-imidazolidinone (DMI) as a solvent and KF as a fluoride ion source (Eq. 38), whereas alkenylsilanes prefer THF and TBAF (Eq. 39). 

Aryl chlorosilanes were found to undergo palladium-catalyzed cross coupling reaction with aryl chlorides in the presence of a fluoride salt giving unsymmetrical biaryls (see Scheme 36 [129]). A variety of functional groups (cyano, acetyl, fluoro, trifluoromethyl) are tolerated in this reaction. While the... 

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