Bromides arylzinc

Arylzinc bromides are also capable of reacting with functionalized primary alkyl iodides in the presence of Ni(acac)2-410 The couplings readily occurred in the presence of an equimolar amount of 4-trifluoromethylstyrene at -15 °C. 

Table 1 Polyfunctional products obtained by the Ni(ll)-cat zedcross<50UFling of Arylzinc bromides and alkyl iodides in the presence of 4-(trifluoromethyl)styrene. 

SCHEME 5. Preparation and uses of functionalized arylzinc bromides using Rieke zinc... 

A variety of additional organozinc-mediated couplings to iT-allylpalladium complexes have been reported, including those of perfluoroalkylzinc iodides,150 vinylzinc bromides,151 allylzinc acetates152 and arylzinc bromides (equations 35-37).153,154... 

In 1973, the direct potassium metal reduction of zinc salts was reported.3 This active zinc powder reacted with alkyl and aryl bromides to form the alkyl- and arylzinc bromides under mild conditions.4 The reduction of anhydrous zinc salts by alkali metals can be facilitated through the use of electron carriers. Lithium and sodium naphthalenide reduce zinc salts to give highly reactive metal powders under milder and safer conditions. Graphite5 and liquid ammonia6 have also been employed as electron carriers in producing zinc powders. A highly dispersed reactive zinc powder was formed from the sodium metal reduction of zinc salts on titanium dioxide.7... 

Electrochemical preparation of an arylzinc bromide and its coupling with 2-chloropyridine synthesis of 2-(4-methoxyphenyl)pyridine... 

Add the catalyst solution to the arylzinc bromide solution at -25°C. Allow to warm to rt, then heat the reaction mixture at 55°C for 10 h. 

Scheme 6.14 Negishi-coupling between arylzinc bromides and arylhalides...

Selective palladium(0)-catalyzed arylation can be performed with aryl iodides bearing a triflate function using an appropriate palladium catalyst. Under these conditions, aromatic iodotriflates like 59 can play the role of multi-coupling reagents [88]. Thus, the reaction of 59 with a functional arylzinc bromide provides the functionalized biphenyl triflate 60 (see Section 9.6.13 Scheme 9-48) [89]. 

Zn alkyls, generated in situ, are very versatile reagents for alkyl-alkyl, alkyl-aryl and aryl-aryl couplings [73]. Arylzinc bromides and benzylzinc iodides may serve as more reactive substitutes for boronates or stannanes in Pd-mediated couplings. 

Carboxylation. Arylzinc bromides undergo carhoxylation with CO2 readily. The Pd catalyst (with Cy3P as hgand) performs better than a similar Ni complex. 

Betzemeier and Knochel performed cross-couplings of aryl iodides with arylzinc bromides in a toluene/l-bromoperfluorooctane mixture in the presence of a Pd catalyst derived from fluorous phosphine la and Pd2(dba)3 (Scheme 1) [15]. The reaction yielded the desired coupling products in excellent yields (87-99%). By using 1.5 mol% of catalyst it was possible to re-use the catalyst up to four times, yielding biphenyl derivative 2. This cross-coupling reaction could be extended to benzyl- and alkenylzinc bromides forming 3 (76%) and 4 (92%). 

Scheme 1 Cross-coupling of aryl iodides with arylzinc bromides.

Scheme 3.13 Cross-coupling of a methoxypyridinium salt with arylzinc bromides.

Scheme 2-88. Preparation of the arylzinc bromide 221 using Rieke-zinc andnd its...

Aromatic ketones are also synthesized efficiently via cobaltcross-coupling reaction from these electrogenerated arylzinc bromides and add cMorides according to [44] ... 

When arylzinc bromide is formed via an electrochemical method using a simple catalytic system involving cobalt halide in acetonitrile as solvent, the use of a supplementary amount of CoXj catalyst is sufficient but necessary to consume all the... 

Then, the use of nickel(II) or cobalt(II) complexes as catalyst associated to the sacrificial anode process allows synthesis of functionalized mono- or diorganozinc species in a simple and efficient manner. Alternating Jt-conjugated copolymers, based on this electrochemical preparation of intermediate aryldizinc species and their subsequent palladium-catalyzed coupling with unsaturated dihalogenated compounds, can be synthesized. Furthermore, aromatic ketones are synthesized efficiently via cobalt-catalyzed cross-coupling reaction between arylzinc bromides and acid chlorides. 

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