Organocadmium compounds reactivity

The success of the last reaction depends upon the inertness of the ester carbonyl groups towards the organocadmium compound with its aid and the use of various ester acid chlorides, a carbon chain can be built up to any reasonable length whilst retaining a reactive functional group (the ester group) at one end of the chain. Experimental details are given for l-chloro-2-hexanone and propiophenone. The complete reaction (formation of ketones or keto-esters) can be carried out in one flask without isolation of intermediates, so that the preparation is really equivalent to one step. 

Organocadmium compounds can be prepared from Grignard reagents or organo-lithium compounds by reaction with Cd(II) salts.180 They can also be prepared directly from alkyl, benzyl, and aryl halides by reaction with highly reactive cadmium metal generated by reduction of Cd(II) salts.181... 

Dialkylcadmium compounds are also reactive towards H2S. For example, (Me3SiCH2)2Cd reacts immediately with H2S to give CdS (equation 19). Other organocadmium compounds with Cd S bonds include the thiocyanate derivatives RCdSCN that are obtained by the reaction of R2Cd with (SCN)2 (equation 20). ... 

Grignard reagents themselves react readily with acid chlorides, but the products are usually tertiary alcohols these presumably result from reaction of initially formed ketones with more Grignard reagent. (If tertiary alcohols are desired, they are better prepared from esters than from acid chlorides. Sec. 20.21.) Organocadmium compounds, being less reactive, do pot react with ketones. 

The comparatively low reactivity of organocadmium compounds not only makes the synthesis of ketones possible, but in addition widens the applicability of the method. Organocadmium compounds do not react with many of the functional groups with which the Grignard reagent does react —NO2, —< N, —CO—, —COOR, for example. Consequently, the presence of one of these groups in the acid chloride molecule does not interfere with the synthesis of a ketone (compare with Sec. 15.15). For example ... 

Burkhardt, E. R., Rieke, R. D. The direct preparation of organocadmium compounds from highly reactive cadmium metal powders. J. Org. Chem. 1985, 50,416-417. 

In an attempt to alleviate the problems associated with the instability of diethyl 1-lithio-l, 1-difluoromethylphosphonate, a study of the reactivity of the corresponding organocadmium compound was performed in 1981. It reacts with a variety of allyl, propargyl, and benzyl bromides or iodides in THF at room temperature to afford the alkylated products in 7-64% yields (Scheme 3.71, M = CdBr, X = Br, I), but these compounds are contaminated with variable quantities of protonated carbanion. ... 

Recent investigations have shown that the reactivity of organocadmium compounds is increased by the presence of magnesium salts if prepared in solution from a Grignard reagent and a cadmium halide, dialkylcadmiums — the members most studied — are appreciably more reactive than pure dialkylcadmiums in ether.158... 

L.M.Dyagileva and Y.A.Aleksandrova, The Reactivity of Organozinc and Organocadmium Compounds in Decomposition Reactions, ... 

Organomercury and organocadmium compounds are much less reactive than the corresponding lithium or magnesium derivatives, and are therefore useful for certain reactions where selectivity is important. One useful synthetic application of this strategy is the preparation of ketones from acid chlorides and cadmium reagents. Cadmium reagents are useful because they are too unreactive to add to the product ketone, and the reaction therefore stops at the ketone. 

Primary alcohols and 1,2-diols are more reactive than secondary alcohols in the case of organozinc compounds while in the case of organocadmium compounds the secondary alcohols are more reactive than primary alcohols, but less reactive than 1,2-diols. 

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