Trans-metallation

However, for the synthesis of alkenylmercuric salts, one difficulty was encountered as mercuric acetate also reacted with the residual double bond. Fortunately, cyclohexene with mercuric acetate in tetrahydrofuran gave only 8 % reaction after 42 h1951. Thus, 2-(4-cyclohexenyl)-ethylmercuric chloride was obtained in 94% isolated yield via hydroboration-mercuration sequence of 4-vinyl cyclohexene (Eq. 123) 192). 

It is to be pointed out that vinylboranes synthesized via hydroboration with di-siamylborane and dicyclohexylborane are less satisfactory and afforded l93) byproducts in addition to the desired frarw-alkenylmercuric acetate. 

We have seen the relative reactivities of structurally different alkenes towards various dialkylboranes vary over a broad range of differences, e.g., disiamylborane 431 and 9-BBN481 vary in a range of 105. This makes selective hydroboration of the more reactive alkenes possible in the presence of less reactive one. Disubstituted internal (Z)-alkenes are more reactive to disiamylborane than their ( T)-isomers (Eq. 125). Recently, it has been observed that the selectivity is much higher with ThxBHCl SMe2 

Terminal alkenes can be removed from mixtures containing internal alkenes43), and trisubstituted alkenes from tetrasubstituted isomers (Eqs 126 and 127)I98). 

The separation of racemic mixture is the most difficult process and involves several steps. The selective hydroboration sequence provides a convenient procedure 199 200 for the resolution of 1,3-disubstituted allenes, while the process is tedious and lengthy by other methods201. Thus, the treatment of ( + )-1,3-dimethyl allene with 50 mol percent of (+)-IPC2BH provided unreacted (R)-(-)-l,3-dimethylallene (Eq. 128). The configuration of allenes is consistently R when resolved by ( + )-IPC2BH. As both forms of IPC2BH are available, it should be possible to obtain the allenes of opposite configuration. 

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Kirkendall E O 1942 Diffusion of zinc in a-brass Trans. Metall. Soo. AIME 147 104... 

Aryl- or alkenylpalladium comple.xcs can be generated in situ by the trans-metallation of the aryl- or alkenylmercury compounds 386 or 389 with Pd(Il) (see Section 6). These species react with 1,3-cydohexadiene via the formation of the TT-allylpalladium intermediate 387, which is attacked intramolecularlv by the amide or carboxylate group, and the 1,2-difunctionalization takes place to give 388 and 390[322]. Similarly, the ort/trt-thallation of benzoic acid followed by transmetallation with Pd(II) forms the arylpalladium complex, which reacts with butadiene to afford the isocoumarin 391, achieving the 1,2-difunctionalization of butadiene[323]. 

A trialkylsilyl group can be introduced into aryl or alkenyl groups using hexaalkyidisilanes. The Si—Si bond is cleaved with a Pd catalyst, and trans-metallation and reductive elimination afford the silylated products. In this way, 1,2-bis-silylethylene 761 is prepared from 1,2-dichloroethylene (760)[625,626], The facile reaction of (Me3Si)2 to give 762 proceeds at room temperature in the presence of fluoride anion[627]. Alkenyl- and arylsilanes are prepared by the reaction of (Me3Si)3Al (763)[628],... 

Stannylation, followed by trans-metallation and subsequent electrophilic quenching, provides a good route (6) to simple functionalized vinylsilanes ... 

Additional coordination upon hydrozirconation (see Scheme 8-13) but also during the subsequent transformations (see Schemes 8-14 and 8-15) has to be taken into account in the analysis of the regiochemistry of the hydrozirconation/trans-metalation reaction sequences. 

Organozinc compounds are more reactive nucleophiles requiring no activation for the trans-metalation step, while allowing for much wider functionality to be present in the molecule than in organomagnesium compounds. However, organozinc compounds cannot be stored without special precautions, and therefore should be generated immediately prior to use, which makes... 

The competitive equilibria based on the different plasma models cannot solely explain the in vivo behaviour of Gd111 complexes. The excretion of low molecular weight Gd111 chelates from the body is very rapid (e.g., t1/2 = 1.6 h for [Gd(DTPA)]2 ),M0 whereas the dissociation and trans-metallation of the Gd111 complexes is relatively slow. Therefore, the system is far from equilibrium and kinetic factors could substantially change the predicted amount of free Gd3+. 

This procedure is more convenient than the conventional method, which involves a trans-metalation reaction from an o -alkoxyalkyltrialkyltin(IV). 

Morkan, I. A. Uztetik-Morkan, A. Trans. Metal Chem. 2003, 28, 182-186. 

Transfer of the acyl group from the acylzirconocene chloride to aluminum (transmetala-tion) by treatment with aluminum chloride has been reported to give an acylaluminum species in situ, and the possibility of the acylaluminum acting as an acyl anion donor has been suggested (Scheme 5.5) [7]. However, the acyl anion chemistry through this trans-metalation procedure appears to be limited since only protonolysis to the aldehyde proceeds in good yield, which could be achieved by direct hydrolysis of the acylzirconocene chloride. 

The use of organozirconium compounds as carbanion equivalents is greatly facilitated by trans metallations to the more reactive aluminum [11,100], copper [104—106], nickel [96—98], and palladium [99] derivatives. Copper-catalyzed carbon—carbon bond-forming reactions of alkyl- and alkenylzirconocene compounds have been particularly well studied, and have found considerable application in organic synthesis [107,108]. 

Vinyl cuprates.17 Vinyl cuprates can be prepared conveniently by in situ trans-metallation of vinylstannanes, available by hydrostannylation of alkynes, with a cuprate such as (CH3)2Cu(CN)Li2 (equation I). Reagents prepared in this way effect conjugate addition of the vinyl group to an enone with essentially no transfer of the methyl group. 

Various intermolecular coupling reactions involving acetylene hydrocarbons have been reported to lead to vinylallenes. For example, 1-phenylpropyne (93), after activation with Hg(II) chloride, is first metalated by butyllithium treatment, then trans-metalated with zinc bromide and finally coupled with 1-iodo-l-phenylethene (94) in the presence of tetrakis(triphenylphosphine)palladium to provide the diphenylvinyl-allene 95 in moderate yield (Scheme 5.12) [31]. 

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