Organocadmium reagents, with

While most of the chemistry discussed in this chapter has been developed in the past decade, several important methods have withstood the test of time and have made important contributions in areas such as natural product synthesis. Methods such as cuprate acylation and the addition of organolithiums to carboxylic acids have continued to enjoy widespread use in organic synthesis, whereas older methods including the reaction of organocadmium reagents with acid halides, once virtually the only method available for acylation, has not seen extensive utilization recently. In the following discussion, we shall be interested in cases where selective monoacylation of nonstabilized carbanion equivalents has been achieved. Especially of concern here are carbanion equivalents or more properly organometallics which possess no source of resonance stabilization other than the covalent carbon-metal bond. Other sources of carbanions that are intrinsically stabilized, such as enolates, will be covered in Chapter 3.6, Volume 2. 

The acylation of organocadmium reagents with acid chlorides such as (115) formed an early method for synthesis of progesterone derivatives such as 21-methyl progesterone (equation 97). The same transformation may be accomplished more easily with palladium-catalyzed organotin acylation in 45%... 

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. 

A cautionary note must be sounded here, the above explanation being slightly oversimplified. First, electrophilic assistance does not necessarily imply 1,2- addition. Michael reactions occur, even in the absence of cryptands Equally, a rigorously purified organocadmium reagent will not react with enones Li+ or Mg2+ impurities are needed to promote the conjugate addition. 

Though the first carbon atoms in LVII and LVIII are asymmetric, only one of the two possible stereoisomers was obtained in each case. It was suggested that the substantial quantities of sirup accompanying the production of these crystalline substances may have contained the other isomer. The authors propose a plausible ionic mechanism for the reaction of organocadmium compounds with tetraacetylglucosyl bromide, leading alternatively to compounds of types IV or LVII. It was reasoned that a carbonium ion was formed at carbon 1 by attack of the cadmium reagent at the bromide function ... 

Alkylation of quinones with organocadmium reagents allows the synthesis of quinol derivatives, without any formation of hydroquinones or bis-addition products (Equation (178)).315 The regiochemistry of the addition is strongly... 

The configuration at the remaining asymmetric center in a-erythro-idine, C-12, was determined by Hill and Schearer (21) who took advantage of the Hofmann degradation sequence carried out earlier (Fig. 4) which had yielded the dextrorotatory ketone XVII (-I- )-XVII was synthesized by reaction of the organocadmium reagent from o-bromoethyl-benzene with the acid chloride from (-I- )-tetrahydrofuran-3-carboxylic acid (LI). The configuration of LI was then established by conversion to (4-)-3-methyltetrahydrofuran which was also prepared from R - -)-... 

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