Cross-coupling Reactions of Aryl Electrophiles

In the event of a first substrate screening, aryl iodides and bromides yielded mainly the reduced compound B with n-C6H13MgBr in presence of catalytic amounts of Fe(acac)3 in THF-NMP at 0°C (Table 5.4, entries 1 and 2). In contrast, the corresponding aryl chloride furnished the desired product in quantitative yield (entry 3) the triflate and even the tosylate, which turned out to be a difficult substrate in nickel- and palladium-catalyzed reactions [24], were converted in high yields (entries 4 and 5). 

Kharasch and co workers reported in a series of classical papers that aryl-Grignard reagents undergo catalytic decomposition with the formation of biaryls in presence 

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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. 

The use of aryl tosylates as electrophiles is attractive, since they can be synthesized from readily available phenols with less expensive reagents than those required for the preparation of the corresponding triflates. More importantly, tosylates are more stable towards hydrolysis than are triflates. However, this greater stability renders tosylates less reactive in transition metal-catalyzed coupling reactions. As a result, protocols for traditional cross-coupling reactions of these electrophiles were only recently developed [1], In contrast, catalytic direct arylations with aryl tosylates were not reported previously. However, a ruthenium complex derived from heteroatom substituted secondary phosphine oxide (HASPO) preligand 72 [81] allowed for direct arylations with both electron-deficient, as well... 

When the metallic additive to the intermediate 374 was zinc dihalide (or another Lewis acid, such as aluminum trichloride, iron trichloride or boron trifluoride), a conjugate addition to electrophilic olefins affords 381 . In the case of the lithium-zinc transmetallation, a palladium-catalyzed Negishi cross-coupling reaction with aryl bromides or iodides allowed the preparation of arylated componnds 384 ° in 26-77% yield. In addition, a Sn2 allylation of the mentioned zinc intermediates with reagents of type R CH=CHCH(R )X (X = chlorine, bromine) gave the corresponding compounds 385 in 52-68% yield. ... 

The alkenylmagnesium species generated by the Fe-catalyzed arylmagnesiation can be trapped by electrophiles. For example, the cross-coupling reaction of the alkenyhnagne-sium species with an aryl halide is achieved with a nickel catalyst, giving a tetrasubstituted olefin 21 in good overall yield (Scheme 17). ... 

When the first electrophile was not a ketone or an aldehyde, as illustrated for the reaction of 276 with crotonyl chloride, the intermediate chelated alkenylmetal 278 could also be subjected to iodinolysis or palladium-catalyzed cross-coupling reactions with aryl and alkenyl iodides in the presence of a stoichiometric amount of CuBr as a promotor as well as a polar cosolvent such as IV, IV-di methyl acetamide (DMA) (equation 131)165 166. 

Palladium(0)-catalyzed cross-coupling reactions between organic electrophiles (usually vinyl or aryl halides or triflates) and a variety of organometallic reagents and boronic acids have become a popular... 

Cyclic sulfamates 48a and 48b (Scheme 8, section 14.08.5.2.1) function as electrophilic partners with Ni-catalyzed cross-coupling reaction of Grignard reagents. This transformation thus offers an easy access to the variety of aryl-substituted amines 49 <2005OL4685>. 

TABLE 1. Pd-Catalyzed Cross-Coupling Reactions of Alkylalnminnnis with Alkenyl and Aryl Electrophiles... 

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