Diarylzinc

Silver aryls are also stable, prepared using either diarylzinc or trialkylaryl-lead (or tin) compounds... 

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%). 

A similar but less useful amination reaction was reported by the Erdik group.426,427 They found that diarylzincs and trialrylzincates reacted with acetone 0-(2,4,6-trimethylphenylsulfonyl)oxime 327 and O-methylhydroxylamine in the presence of GuGN. The products of this reaction were hydrolyzed to afford the corresponding primary amines in modest yield (Scheme 167). 

The third reaction pathway involves the redistribntion reaction of a diaUcyl- or diarylzinc compound with a zinc salt. An example of this ronte is the formation of the nnsolvated organozinc halides EtZnCl, EtZnBr and EtZnI from the reaction of pure EtiZn with the corresponding zinc halide in a 1 1 ratio ... 

In general, simple dialkylzinc and diarylzinc compounds are monomers in which the zinc atom, as a consequence of its ground-state electronic configuration, is sp hybridized. Thus, such molecules contain a linear C—Zn—C arrangement. The only known exception to this rule is diphenylzinc, which in the solid state is a dimer formed via electron-deficient /r -bridging phenyl groups. 

Since the isopropyl group is also transfeired in the reaction with an electrophile at a comparable rate as the second R group, an excess of electrophile must be added and tedious separations may be required. A more straightforward approach is possible for diarylzincs. In this case, the l/Zn exchange can be performed under very mild conditions . 

SCHEME 39. Functionalized diarylzincs bearing an aldehyde or an isothiocyanate functional group... 

Nowadays, this chemistry includes a wide range of applications. The organozinc compounds employed in the enantioselective addition include dialkylzincs, dialkenylzincs, dialkynylzincs, diarylzincs and the related unsymmetrical diorganozincs. Electrophiles have been expanded to aldehydes, ketones and imines. Asymmetric amplification has been observed in the enantioselective addition of organozincs. Recently, asymmetric autocatalysis, i.e. automultiplication of chiral compounds, has been created in organozinc addition to aldehydes. 

In conclusion, the electrosynthesis of diarylzinc or diheteroaryl zinc species can be achieved with good yields to the reaction conditions described above to the presence of 10 or 20% of catalyst and using the corresponding dibromides or sometimes dichloride reagents. 

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). 

A rhodium-chiral phosphine complex catalyzes the enantioselective addition of phenylboronic acid to 1-naphthaldehyde to give a chiral diaryl carbinol but with moderate ee (Scheme 13) [39]. When considering the introduction of functionalized aryl groups, arylboronic acid is a promising alternative arylating reagent to diarylzinc compounds. 

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

Homoleptiic dialkylzinc compounds, characteristics, 2, 317 Homoleptiic diarylzinc compounds, characteristics, 2, 320 Homologation, B-C bonds, 9, 175 Homolytic cleavage... 

Diarylzinc compounds react with silver salts to give arylsilver compounds of high purity and stability (Scheme 1.15).52 Van der Kerk and coworkers synthesized phenylsilver and a number of methyl-substituted arylsilver compounds via this route, and found that ortho-methy substitution significantly increased the thermal stability of the compound, as is the case for the corresponding arylcopper compounds (Table 1.5).53... 

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