Stereochemistry optical isomerism

The stereochemistry of products relative to starting materials can give important clues to the structure of the transition state. The stereochemistry of molecules gives rise to two types of isomerism optical isomerism (cnantiomcrismjand geometrical isomerism. 

The Atlas of Stereochemistry lists the absolute configurations of about 3000 organic substances, with derivations. Apart from optical isomerism, it lists many examples whose chirality is owed to isotopic substitution, to chiral axes or planes, or to chiral centres other than carbon (Klyne and Buckingham, 1978). 

William E. Colley, Chui Fan Liu and J. C. Bailar, Jr., The Stereochemistry of Complex Inorganic Compounds. XXIII. Double Optical Isomerism and Optical-Geometric Isomerism in Cobalt(III) Complexes, J. Am. Chem. Soc. 81 4189 (1959). 

Even before he received his doctorate he had publidied work on the stereochemistry of organic compounds. He accounted for the phenomenon of optical isomerism with his ideas on the tetrahedral arrangement of the bonding around a carbon atom. He shares the honour of this original idea with the French chemist Joseph Le Bel who independendy came up with the same idea. 

The most common coordination number is six and such complexes have an octahedral structure. The next most common four-coordinated systems have either tetrahedral or square planar structures. Other complexes are known having different coordination numbers and structures. The stereochemistry of metal complexes is a fascinating subject. Several different types of isomeric structures are possible and have been demonstrated in these systems. For our purpose here it is sufficient to cite examples of geometrical (ds-trans) and optical isomerism. This can readily be iUustrated by the cis (III) and trans (IV) isomers of QCo(en)2Cl2]+. Note that the... 

The stereochemistry of pyrazolines and pyrazolidines has already been discussed (Section 4.04.1.4.3). Optically active A - and A -pyrazolines have seldom been described (77JA2740, 79CJC360), but cis-trans isomeric pairs are common. The C-4 acid-catalyzed epimerization involves the mechanism shown in Scheme 38 (70TL3099), but in spite of some inconclusive arguments the C-5 epimerization has never been established with certainty. 

Chromium, tetraaquadichloro-chloride dihydrate hydrate isomerism, 1, 183 Chromium, tetrabromo-solvated, 3, 758 synthesis, 3, 763 Chromium, tetrachloro-antiferromagnetic, 3, 761 ferromagnetic magnetic properties, 3,7559 optical properties, 3,759 structure, 3,759 solvated, 3. 758 synthesis. 3, 759 Chromium, tetrachlorooxy-tetraphenylarsenate stereochemistry, 1,44 Chromium, tetrahalo-, 3,889 Chromium, tetrakis(dioxygen)-stereochemistry, 1,94 Chromium, triamminediperoxy-structure. 1, 78 Chromium, tricyanodiperoxy-structure, 1, 78 Chromium, trifluoro-electronic spectra, 3, 757 magnetic properties, 3, 757 structures, 3, 757 synthesis, 3, 756 Chromium, trihalo-clcctronic spectra, 3, 764 magnetic properties, 3, 764 structure, 3, 764 synthesis, 3, 764 Chromium, tris(acetylacetone)-structure. 1, 65 Chromium, tris(bipyridyl)-... 

A number of examples involving the stereochemistry of five membered rings are met in furanose sugars. An interesting example is that of 2, 5 dimethylcyclopentane 1, 1 dicarboxylic acid. This acid can exist in two geometrically isomeric forms which can be distinguished by decarboxylation. The cis xxvii isomer forms two monocarboxylic acids which are meso because they possess a vertical plane of symmetry. The trans isomer xxviii forms only one monocarboxylic acid and since it possesses no elements of symmetry, therefore, exists in optically active forms and a meso variety. 

In 1990, Ito and Furukawa reported the isolation of furostifoline (224) and the isomeric eustifoline-D (227) from the root bark of M. euchrestifolia. These were the first furocarbazole alkaloids obtained from a natural source (101). Seven years later, Wu et al. reported the isolation of further furocarbazole alkaloids, furoclausine-A (225) and furoclausine-B (226) from the root bark of a different plant source, C. excavata (128). Furoclausine-B (226) was isolated from nature in optically active form [mId -32.73 (c 0.022, MeOH), however, the absolute stereochemistry is not known (128,175,176) (Scheme 2.55). 

Tnformation about the characteristics of keto-hexoses in solution has been - derived mainly from optical rotatory data (I, 2, 3, 4) and in recent years by application of the principles of conformational analysis (5, 6). In the current study an attempt is made to describe the conformation and composition of these sugars in solution by nuclear magnetic resonance (NMR) spectroscopy, a highly sensitive means for examining stereochemistry and for differentiating between isomeric species. 

Optically active aldehydes can be obtained by asymmetric hydroformylation of olefinic substrates when at least one asymmetric carbon atom is formed either by addition of a formyl group or of a hydrogen atom to an unsaturated carbon atom (Scheme 1, reactions (1) and (2)). In the case of trisubstituted olefins, two new asymmetric carbon atoms can form due to the cis stereochemistry of the reaction10), in the absence of isomerization, the formation of only one epimer is expected. 

The first detailed stereochemical investigation of an ene reaction was reported in 1980 [52], In this study the correlation between the stereochemistry of C—O bond-making to C—H(D) bond-breaking in the ene reaction was investigated. This intriguing experiment was performed by combining stereoisotopic studies in the photo-oxygenation reaction of the optically and isomerically pure olefins 1 and 2 ... 

Allylic double bonds can be isomerized by some transition metal complexes. Isomerization of alkyl allyl ethers 480 to vinyl ethers 481 is catalysed by Pd on carbon [205] and the Wilkinson complex [206], and the vinyl ethers are hydrolysed to aldehydes. Isomerization of the allylic amines to enamines is catalysed by Rh complexes [207]. The asymmetric isomerization of A jV-diethylgeranylamine (483), catalysed by Rh-(5)-BINAP (XXXI) complex to produce the (f )-enaminc 484 with high optical purity, has been achieved with a 300 000 turnover of the Rh catalyst, and citronellal (485) with nearly 100% ee is obtained by the hydrolysis of the enamine 484 [208]. Now optically pure /-menthol (486) is commerically produced in five steps from myrcene (482) via citronellal (485) by Takasago International Corporation. This is the largest industrial process of asymmetric synthesis in the world [209]. The following stereochemical corelation between the stereochemistries of the chiral Rh catalysts, diethylgeranylamine (483), diethylnerylamine (487) and the (R)- and (5)-enamines 484... 

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