Alkylzinc iodide

The organization of the material in this chapter is naturally subjective, and certain topics could equally well have been discussed in another section or in a different order. For example, the Simmons-Smith reagent is both an alkylzinc iodide and a carbenoid, and because both sections exist in this chapter, it is discussed under the more specific heading of zinc carbenoids. 

Nickel and palladium complexes catalyze the conversion of alkyl iodides to alkylzinc iodides 30 with added diethylzinc (Scheme 28).74 Thus, for example, 1-iodooctane was converted at room temperature to n-octylzinc iodide after treatment with 2 equiv. of diethylzinc in the presence of 1.5 mol% of a palladium bis(phosphine) complex. 

Charette et al. converted both primary and secondary alkyl iodides to the corresponding alkylzinc iodides, using either ethylzinc iodide or isopropylzinc iodide.34 The reactions, for example, Scheme 30, which were performed in UV-irradiated (X > 280 nm) chloroform solutions, gave conversions as high as 88% in less than 4h. 

Primary and secondary alkylzinc iodides and benzylic zinc halides also undergo Ni-catalyzed reactions with various primary alkyl iodides and bromides.407-409 According to the procedure by Knochel and co-workers, the transformations with alkylzinc iodides, which are less reactive than the corresponding dialkylzincs, require the presence of two additives Bu4NI and 4-fluorostyrene (Scheme 155).407,408... 

Alkylzinc iodides These reagents are prepared by reaction of alkyl iodides with Zn/Cu in toluene-N,N-dimethylacetamide (DMA). In the presence of 1 equiv. of chlorotrimethylsilane they can add to aldehydes to form alcohols. DMA may be replaced as the cosolvent by N-methylpyrrolidone (NMP), but HMPT retards this reaction. This reaction can be used to obtain y-, 8-, and e-hydroxy esters from P-, y-, and 8-zinc esters (equation I). 

In the case of an intramolecular 1,4-addition, no activation is required . The iodoenone 238 is readily converted into the conesponding alkylzinc iodide, which undergoes an intramolecular addition at 25 "C in THF affording the bicyclic ketone 239 in 65-67%... 

H. P. Berger, S. Knochel, P. Preparation and reactivity of chiral /3-amido-alkylzinc iodides and related configurationally stable zinc orga-nometallics. Tetrahedron 1994, 50, 2415-2432. 537... 

As a final illustration of the tremendous functional group compatibility of alkylzinc iodides, the preparation of a protected tso-dityrosine derivative is described in Protocol 7.23 This procedure is noteworthy in the that it illustrates the possibility of inserting zinc selectively into an aliphatic carbon-iodine bond in the presence of an aromatic carbon-iodine bond. This stands in sharp contrast to the situation described in Protocol 4 where excess zinc can react with the electrophile, and must therefore be removed. The selectivity of... 

Copper-mediated addition of a functionalized alkylzinc iodide to an acid chloride preparation of 4-oxocyclohexyl 5-phenyl-5-oxopentanoate2... 

Copper-mediated conjugate addition of an alkylzinc iodide to a nitro olefin preparation of 1-chloro-5-(nitromethyl)octaneZ0... 

Add the solution of the alkylzinc iodide to the CuCN 2LiCI solution. Allow to warm to 0°C, stir for 5 min, and cool the resulting light green solution to... 

Confirm the alkylzinc iodide formation by performing an iodolysis and a hydrolysis as described in Protocol 1. 

The preparation of alkylzinc iodides is facilitated if the reaction is performed in THF and NMP mixtures. Such solutions of Me02C(CH2)4ZnI add to benzaldehyde in the presence of TMSCI (2 equiv.) in 70% yield.33 The use of ultrasound also promotes the formation of organozinc compounds.34>34a 34e This procedure proved to be especially useful for the preparation of Jackson reagent 6 derived from serine. In the presence of a copper(l) or palladium(O) catalyst, this zinc derivative reacts with various electrophiles (Scheme 1) 3S,3Sa-3Sj 0f z nc reagent 7 leading to methyl but-3-enoate and the zinc amide... 

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. 

An important development in cuprate acylation methodology that addresses several of the most objectionable properties of the reagents themselves has come from Knochel and his associates.New highly functionaliz copper reagents, represented by the formula RCu(CN)ZnI, can be prepared from readily available primary and secondary alkylzinc iodides by transmetallation with the soluble complex CuCN-2LiX in THF (equation 65). 

Primary and secondary alkylzinc iodides (RZnI) are best prepared by direct insertion of zinc metal (zinc dust activated by 1,2-dibromoethane or chlorotrimethylsilane) into alkyl iodides or by treating alkyl iodides with Rieke zinc. The zinc insertion shows a remarkable functional group tolerance, permitting the preparation of polyfunctional... 

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