Cross-coupling reactions arylsilane

Han, Y. Walker, S. D. Young, R. N. Silicon Directed ipso-Substitution of Polymer Bound Arylsilanes Preparation of Biaryls via the Suzuki Cross-Coupling Reaction, Tetrahedron Lett. 1996, 37, 2703—2706. 

Han Y, Walker SD, Young RN, Silicon directed ipso-substitution of polymer bound arylsilanes preparation of biaryls via the Suzuki cross-coupling reaction, Tetrahedron Lett., 37 2703-2706, 1996. 

Table 1 Pd-catalyzed cross-coupling reactions of alkenyl- and arylsilanes...

Synthetic reactions involving activation of alkenyl- and arylsilanes by copper salts have also been reported. A copper-mediated system is effective in the cross-coupling reaction of aryl- and heteroarylsilanes with aryl halides under Pd-free conditions (Equation (13)).66 Alkenyl- and arylsilanes as well as alkynylsilanes undergo homocoupling in the presence of Cul and air.65,65a Functionalized alkenyl- and arylsilanes bearing a coordination site in the vicinity of silicon (e.g., 7) are easily activated by copper salts even at room temperature (Scheme 5).67,67l 67e 68 q-jle organocoppers such as 8 are useful for carbon-carbon bond-forming reaction with carbon electrophiles. 

We have found that alkynylsilanes are smoothly converted into alkynylcopper compounds by treatment with CuCl in l,3-dimethyl-2-imidazohdinone (DMI) the copper reagents can be isolated in good yields [563]. This study was the first example of preparation and isolation of organocopper compounds by use of organosilicon reagents. The Si-Cu transmetalation is applicable to the synthesis of alkynyl ketones by Cu-catalyzed alkynylation of acid chlorides (Scheme 10.217). We have also shown that a Cu-mediated system is effective in the cross-coupling reaction between arylsilanes or heteroarylsilanes and aryl hahdes [564]. 

Cross-coupling reactions of arylsilanes with aryl halides... 

The cross-coupling reaction of aryl halides with arylsilane reagents is an important alternative aryl-aryl bond forming strategy. Thus the reaction of various aryltrialk(ox)ylsilanes readily proceeds with aryl iodides [130] and bromides [131] in the presence of palladium(0)-catalyst to give the biaryls in good to excellent yields. Scheme 32. 

Many arylations are assisted by functional groups that promote ortho-metallation. Thus, for example, acetanihdes react with arylsilanes at the ortho position via pal-ladacycles 78 and 79 to form derivatives 80 (Scheme 11.27) [84]. Mechanistically, this transformation is similar to a cross-coupling reaction, in which the oxidative addition step is replaced by the ortho-metallation, although in this case the Pd(0) intermediate must be oxidized in situ to generate the reactive Pd(ll) species. Unsubstituted benzylamines and N-methylbenzylamine are ortho-arylated with Pd(OAc)2 in the presence of trifluoroacetic acid (TFA) and silver acetate [85], and a mechanism which differs from the usual Pd(0)/Pd(II) catalytic cycle was suggested for this. Ortho-alkylation was also observed in the palladium-catalyzed... 

Hosomi and coworkers described the cross-coupling reaction between arylsilanes or heteroarylsilanes and aryl halides mediated by a copper(I) salt. In particular, the cross-coupling reaction of 2-TST (1) with iodobenzene under fluoride- and palladium-free conditions (eq 31) was examined employing different solvents and copper(I) salts (Table 1). The yield of the product was increased in polar solvents such as 1,3-dimethyl-2-imidazolidinone (DMI). In addition, it was found that the reaction was best promoted by CuOCgFs because of the strong affinity of pentafluorophenoxide ion to the silicon atom, resulting in an accelerated transfer of the thiazole group to copper. 

Cross-Coupling Reaction of 2-(2-Hydroxyprop-2-yl)cyclohexyl-Substituted Arylsilanes with Aryl Chlorides A General Procedure ... 

During the silylation with hexamethyldisilane, the reductive dehalogenation and the formation of a biaryl are common side-reactions. However, these can be minimized by using potassium carbonate as the base in the case of electron-rich substrates, or with potassium fluoride in the reactions with electron-poor substrates. The arylsilanes produced by any of above mentioned reactions can be cross-coupled with aryl hahdes by employing the following methods. Table 9. 

Similar palladium-catalyzed arylation reactions using arylsilane and arylzinc reagents are also possible by the judicious choice of bases and additives. As shown in Equation 5.9, the addition of a fluoride donor BU4NF promoted efficient cross-couplings of primary aUcyl bromides and iodides with aryltrimethoxysilanes [12]. While the reaction showed good functional group compatibility, electron-deficient arylsilanes, such as 4-fluorophenyltrimethoxysilane, showed a rather poor reactivity. 

Protiodesilylation of the starting material is occasionally encountered in the coupling reactions of arylsilanes with a nucleophihc promoter. This side-reaction can be suppressed by the use of a stoichiometric amount of a copper(I) salt to promote the cross-coupling of arylsilyl ethers with iodoarenes (Scheme 7.36) [63]. The preferred salt is CuOCgFj, generated in situ by mixing Cul and NaOC Fj, to effectively promote this reaction. Unhke other arylsilyl ether cross-couphng reactions wherein a trialkoxysilane is used, the mono-methoxysilane reacted much more efficiently than either the di- or trimethoxysilane. Despite the harsh conditions used, this is an impressive fluoride- and paUadium-ffee reaction. 

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