Diarylzinc reagents

Recently, a new method for synthesis of tertiary amines 326 from iV,iV-dialkyl O-benzoyl hydroxylamines 325 was proposed.425 The protocol is based on the copper-catalyzed reaction of hydroxylamines 325 with dialkyl- and diarylzinc reagents (Scheme 166). It is noteworthy that alkyl- and phenylzinc halides also reacted with compounds 325, however, yields were significantly lower than those for ZnR2 (18-29% vs. 69-98%). 

Finally, a recently reported copper catalyzed carbon-nitrogen bond forming process utilises reagents with polarity opposite to the common disconnection protocols. An electrophilic nitrogen, in most cases an (9-acyl hydroxylamine derivative, was successfully coupled with diarylzinc reagents in the presence of copper triflate or copper chloride. Di(2 -pyridyl)zinc and TV-benzoyloxy-morpholine were reacted at ambient temperature in the presence of 1% copper(I) triflate to give 2-morpholinopyridine in 71% yield (7.81.), Under these mild conditions the reaction was over in less than one hour.103... 

Conjugate addition to enals. In the presence of Ni(acac), diarylzinc reagents undergo 1,4-addition to a, 3-enals in satisfactory yield however, the same reaction with dialkylzinc reagents gives low yields (15%, one example). 

Table 5.10 Cross-coupling reaction of sp3 electrophiles with diarylzinc reagents reported by Nakamura et al.

RiZn. Dialkylzinc reagents can be prepared from an organic halide, lithium wire, and zinc bromide at 0° in toluene-THF by sonication in a cell-disruptor generator. Yields are essentially quantitative. Diarylzinc reagents and dimethylzinc can be prepared by sonication in an ultrasonic laboratory cleaner. 

A-Arylindoles and A-arylimidazoles were prepared from aryl halide using a copper catalyst. Diarylzinc reagents react with A-(OBz) amine derivatives, with a copper catalyst, to give the A-aryl amine. " ... 

General procedure for the copper-catalyzed amination offunctionalized diarylzinc reagents. N-(2-Nitrophenyl)-dibenzylamin ... 

The oxidative reaction of amides with diarylzinc reagents was reported by Ackermann [27], The use of a bidentate directing group containing a triazole moiety (TAM) was crucial for the efficiency of the reaction (Eq. 7). 

Aromatic iodides are less reactive toward iodine-zinc exchange. However, preparatively useful reactions can be conducted with iPtjZn or sBUjZn in the presence of catalytic amounts of li(acac) (Scheme 4.20) [93]. This method is quite general for the preparation of functionalized diarylzinc reagents such as 83-86. 

Notably, the presence of iPrI in the reaction medium (generated during the arylzinc preparation or included as an additive) accelerates the cross-coupling reaction, possibly by radical catalysis ]130]. Aromatic and heteroaromatic bromides react with diarylzinc reagents at 25 °C within minutes to yield the corresponding biaryl compounds, as shown with the preparation of 144 from 142 with 143. 

Moreover, the a-selective allylation of diarylzinc reagents can be carried out in good yields using Co(acac)2 as catalyst in NMP at 0 °C (Scheme 4.64) [215]. 

In 2009, Chatani and Tobisu [180] found that the C-H arylation of electron-deficient heteroarenes such as quinolines and pyrazines can be achieved with diarylzinc reagents in the presence of a Ni /PCyj catalyst. In 2010, Zhang... 

The more recent development of NHC ligands, such as those derived from the imidazolium salt L30, has allowed the addition of dialkylzinc (Scheme 63) and diarylzinc reagent (Scheme 64) to simple unactivated p-substituted cyclic enones [98]. Very good yields and enantioselectivities are obtained with a wide variety of organozinc compounds only the less reactive MeaZn does not provide any conversion. 

Scheme 64 CoppCT-NHC-catalysed ECA of diarylzinc reagents to p-substituted cyclic enones by Hoveyda [98]...

Preparation of the functionalized diarylzinc reagent 269 via nucleophilic catalyzed I/Zn exchange reactionf ... 

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