Trans-Cyclopropane- 1,2-dicarboxylic acids

Chrysanthemum dicarboxylic acid or pyrethric acid may exist in eight stereoisomers, owing to the trans or cis configuration on the side chain of the double bond as well as that of the cyclopropane. The natural acid has been shown to be the trans-trans acid. As in the case of the chrysanthemum monocarboxylic acid, the naturally occurring configuration is more insecticidally active than the racemic form or any of the three isomers synthesized. 

FIGURE 1.15 Isomers of cyclopropane-l,2-dicarboxylic acid, (a) Trans isomer (b) meso isomer. 

However, when the two substitutes are same as in cyclopropane 1, 2-dicarboxylic acid (xxiv), we will again have two geometrical isomers cis and trans, but because the molecule contains two similar chiral centres ( ), we will have (+) and (-) forms coming from the trans only along with its racemic variety. The cis form, having a (vertical) plane of symmetry will represent the mesovariety. Therefore, the condition is the same as in tartaric acid. 

The same stereochemical principles apply to both acyclic and cyclic compounds. With simple cyclic compounds that have little or no conformational mobility, it can even be easier to foUow what is going on. Let us first look at cyclopropane-1,2-dicarboxylic acid. These compounds were considered in Section 3.4.3 as examples of geometric isomers, and cis and trans isomers were recognized. 

FIGURE 1.16 Isomers of cyclopropane-1,2-dicarboxylic acid, (a) is-l,2-Dicarboxycyclopropane (trans isomers) (b) Z-l,2-Dicarboxycyclopropane isomer, (meso isomer) (c) Molecular models of E- (trans-) 1,2-dimethylcyclo-propane shown in the tube representation. Rotation of the right hand structure about a vertical axis through the center of the cyclopropane will superimpose the two methyl groups. The methylene of the rotated structure will be in the back, rather than the front, and not superimposed, (d) A mirror plane through the methylene and the back carbon-carbon bond is a plane of symmetry. The two carboxyl groups appear not to reflect each other in the model shown but they can rotate freely and will reflect each other on an instantaneous basis. 

Determinations of absolute configurations of trans-cyclopropane-l,2-dicarboxylic acids on the basis of a definite Cotton effect seem to be possible for carboxylic acid thioamides. In these molecules, such as 123a and 123b, there is a Cotton effect near 330 nm which results from the (n, n ) excitation of the thioamide chromophore . In the... 

Tricarbonyliron complexes of conjugated trienes react with diazoalkanes at the free (uncom-plexed) double bond. In the synthesis of dimethyl 2-formylcyclopropane-l, 1-dicarboxylate (48), the ceric ion served the double function of catalyzing the deazetization and removing the tricarbonyl iron protecting group. When the optically active iron carbonyl complex was used, the addition of diazomethane gave selectively one diastereomer and this was used to make optically active dimethyl 2-formylcyclopropane-l,1-dicarboxylate (>90% ee). A similar route was employed to make the optically active formyl cyclopropanes 49, precursors to optically active cis- and tran.v-chrysanthemic acids. 

Witten et al. (1973) identified adipic and 3-methyladipic acids and also reported the presence in urine, using GC-MS, of aconitic and isocitric acids in addition to citrate. Mamer et al, (1971) reported the occurrence of several hydroxyaliphatic acids in addition to those already identified by other workers, and Mamer and Tjoa have identified 2-ethylhydracrylic acid in urine derived from isoleucine metabolism (Mamer and Tjoa, 1974). Urine from healthy children and adults may contain low amounts of aliphatic dicarboxylic acids of chain length C4-C8 (Lawson et ai, 1976). Pettersen and Stokke (1973) reported a series of 3-methyl-branched C4-C8 dicarboxylic acids in urine from normal subjects, and Lindstedt and co-workers have identified other dicarboxylic acids with cyclopropane rings and acetylenic bonds as well as a series of cis and trans mono-unsaturated aliphatic dicarboxylic acids (Lindstedt et al., 1974,1976 Lindstedt and Steen, 1975). 

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