Dialkylzinc compounds reaction

The direct reaction of zinc metal with organic iodides dates back to the work of Frankland(67). Several modifications have been suggested since that time to increase the reactivity of the metal. The majority of these modifications have employed zinc-copper couples(68-72), sodium-zinc alloys(73), or zinc-silver couples(77). Some recent work has indicated that certain zinc-copper couples will react with alkyl bromides to give modest yields of dialkylzinc compounds(74,73). However, all attempts to react zinc with aryl iodides or bromides have met with failure. The primary use of zinc couples has been in the Simmons-Smith reaction. This reaction has been primarily used with diiodomethane as 1,1-dibromides or longer chain diiodides have proven to be too unneactive even with the most reactive zinc couples. 

In terms of their chemical behavior, dialkylzinc compounds generally react to transfer alkyl groups to other metals. Dialkyls of cadmium are usually prepared by the reaction of a Grignard reagent with a cadmium halide. 

Nucleophilic addition of metal alkyls to carbonyl compounds in the presence of a chiral catalyst has been one of the most extensively explored reactions in asymmetric synthesis. Various chiral amino alcohols as well as diamines with C2 symmetry have been developed as excellent chiral ligands in the enantiose-lective catalytic alkylation of aldehydes with organozincs. Although dialkylzinc compounds are inert to ordinary carbonyl substrates, certain additives can be used to enhance their reactivity. Particularly noteworthy is the finding by Oguni and Omi103 that a small amount of (S)-leucinol catalyzes the reaction of diethylzinc to form (R)-l-phenyl-1 -propanol in 49% ee. This is a case where the... 

The complex of Me2Zn with (5, 5 )-ebpe, 107, has been applied successfully as catalyst in the enantioselective reduction of ketones by polymethylhydrosiloxane and combines excellent product yields with high ee values . Its structure comprises the iV,iV-chelate coordination of the ebpe ligand to the MeiZn unit (Figure 51). It is remarkable that in this case the two secondary amine functionalities are coordinated to zinc and leave the Zn—C bonds unaffected. Indeed, usually secondary amines undergo a fast deprotonation reaction with dialkylzinc compounds. 

A novel approach to allenylzinc reagents, reported by Oku and coworkers, employs propargylic mesylates as starting materials12. Treatment with triorganozincates, prepared in situ by the reaction of dialkylzinc compounds with organolithium reagents, affords transient allenyl dialkylzinc intermediates. These intermediates were found to react with various... 

In another study Feringa et al. [20] reported a catalytic enantioselective three-component tandem conjugate addition-aldol reaction of dialkyl zincs. Here, zinc enolates were generated in situ via catalytic enantioselective Michael addition of dialkylzinc compounds to cydohexenone in the presence of a chiral Cu catalyst. Their diastereoselective reaction with an aldehyde then gave trans-2,3-disubstituted cyclohexanones in up to 92% yields and up to >99% ees (Scheme 9.11). 

Boudier, A. Darcel, C. Flachsmann, F. Micouin, L. Oestreich, M. Knochel, P. Stereoselective preparation and reactions of configurationally defined dialkylzinc compounds. Chem. Eur.J. 2000, 6, 2748-2761. 

Zinc-containing C nucleophiles, which tolerate the presence of diverse functional groups, are not limited to the cited Knochel cuprates obtained from alkyl iodides. The other zinc-based C nucleophiles, which can contain a comparably broad spectrum of functional groups, are dialkylzinc compounds. They are best prepared from terminal alkenes. Figure 10.39 shows in the first two reactions how this is done. 

Ketone synthesis.4 Ketones can be prepared, generally in high yield, by a palladium-catalyzed reaction of acid chlorides with dialkylzinc compounds, prepared in situ by... 

Other transition metals see Transition Metals) such as PdCl2(dppf) and Ni(acac)2 catalyze the reaction but lead to alkylzinc iodides instead of dialkylzinc compounds. 

Preparation. The synthesis of alkylzinc alkoxides and aryloxides is achieved by an alkane elimination process in the simple reaction of a dialkylzinc compound, R2Zn, with one equivalent of an alcohol, R OH (equation 18). This reaction proceeds either in hydrocarbon solvents or neat solution, to give essentially quantitative yields of the desired products. The volatility of the RH side product helps to drive the equilibrium to the right. The formation of relatively strong Zn-O and C-H bonds, at the expense of breaking the O-H and a relatively weak Zn-C bond also guarantee favorable reaction energetics. 

The title compounds are usually obtain in a straightforward manner and in almost quantitative yields by alkane elimination process between a dialkylzinc compound ZnRs and the desired thiol R SH or selenol R SeH species (equation 18). This reaction works equally well in hydrocarbon solvent or neat solution. If thiocyanogen (SCN)2 is used as the reagent, then alkylzinc thiocyanate derivatives (RZnSCN) are obtained. ... 

Even though zincation of secondary amines was already studied by Frankland in 1856 and 1867, it is only in the past few decades that some efforts were made to isolate and characterize the products. Numerous compounds of the type RZnNR2 or Zn(NR2)2 can now be prepared nsing two principal procedures, namely the zincation of amines with simple dialkylzinc compounds " (equation 26) and the metathesis reaction of alkali metal amides with anhydrons zinc dihalide (equation 27). 

A very fast reaction occurs between dialkylzinc compounds and the more acidic amide and thioamide derivatives of the... 

Some heteroleptic (see Heteroleptic Compound) alkylzinc amides have been prepared by addition reaction of dialkylzinc compounds (ZnR2) on l,4-di-tert-butyl-l,4-diaza-l,3-butadiene (t-BuN=CHCH=N-t-Bu). Extensive studies ... 

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