Ketones reactions with organocadmium compounds

P orniation of ketones. Reaction with organocadmium compounds. Discussed in Sec. 19.7. 

Aliphatic ketones are readily prepared from the corresponding secondary alcohols, if these are available. More complicated aliphatic ketones can be prepared by the reaction of acid chlorides with organocadmium compounds. A... 

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. 

The most common application of organocadmium compounds has been in the preparation of ketones by reaction with acyl chlorides. A major disadvantage of the use of organocadmium reagents is the toxicity and environmental problems associated with use of cadmium, and this has limited the recent use of organocadmium reagents. 

Many organocadmium compounds are known but few have been of commercial importance. Wanklyn first isolated diethyl cadmium in 1856. The properties of this and other dialkylcadmiums are listed in Table 4. In general, these materials are prepared by reaction of an anhydrous cadmium halide with a Grignard or alkyUithium reagent followed by distillation of the volatile material in an inert atmosphere or in vacuo. Only the liquid dimethyl compound is reasonably stable and then only when stored in a sealed tube. Dimethylcadmium is mildly pyrophoric in air and produces dense clouds of white, then brown, cadmium oxide smoke, which is highly toxic if breathed (45). When dropped into water, the liquid sinks in large droplets that decompose with a series of small explosive jerks and pops. For this reason, and particularly because of the low thermal stability, most dialkylcadmium materials are prepared and used in situ without separation, eg, in the conversion of acid chlorides to speciality ketones (qv) ... 

Grignard reagents derived from aryl bromides are readily prepared and may be converted into organocadmium compounds by treatment with cadmium chloride (cf. Section 5.8.4, p. 616). Reaction of an organocadmium with a carboxylic acid chloride constitutes a convenient synthesis of aryl alkyl ketones. 

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. 

Lithium bromide [1, 604, before references]. This halide markedly promotes the reaction of an organocadmium compound with acyl chlorides (but not with ketones). The effect was used to advantage in the synthesis of a-oxo esters.8... 

The most common application of organocadmium compounds has been in the preparation of ketones by reaction with acid chlorides. 

The use of organocadmium compounds, RjCd, lies in the fact that they react only with acid chlorides and no other carbonyl compounds. Thus, acid chlorides can be converted to ketones with no risk of further reaction. Organocadmium compounds are prepared (Equation 15.3) by reaction of cadmium chloride with a Grignard reagent, and the reactions only work well when R is aryl or primary alkyl. An example is provided in Figure 15.45. 

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