Stereoisomerism compounds

Clearly, the next step is the handling of a molecule as a real object with a spatial extension in 3D space. Quite often this is also a mandatory step, because in most cases the 3D structure of a molecule is closely related to a large variety of physical, chemical, and biological properties. In addition, the fundamental importance of an unambiguous definition of stereochemistry becomes obvious, if the 3D structure of a molecule needs to be derived from its chemical graph. The moleofles of stereoisomeric compounds differ in their spatial features and often exhibit quite different properties. Therefore, stereochemical information should always be taken into ac-count if chiral atom centers are present in a chemical structure. 

By heat, ocimene is converted into allo-ocimene, which is probably a stereoisomeric compound. 

The procedure used in the preceding sections for cyclopropane serves equally well in the analytic determination of the numbers of structure and stereoisomeric compounds which obtain when essentially different radicals of valence one or alkyl radicals are substituted in the basic compound. We have to assume, however, that there is enough information on the basic compound to determine the three groups discussed in Sec. 56. This is certainly the case for the most important basic compounds, benzene and naphthalene. I omit the formulation of rules which are obvious in the preceding example. 

The fact that from the ionized ester 46 mainly QHj is eliminated whereas the stereoisomeric compound 47 decomposes preferentially via CH3 loss24 is best explained23 by the operation of a two-step process (12). The regiospecific hydrogen transfer 46->48 is responsible for C2H5 loss, whereas CH3 is likely to be eliminated from the intermediate 50. It should be mentioned that the different reactivities of the... 

Tetrazine (171) and its derivatives are electron-deficient cycloaddends, which undergo [4 + 2] cycloadditions with inverse electron demand. When bicyclopropylidene (3) was added to a dichloromethane solution of 171, its red color disappeared within 1.5 h at room temperature. The white crystalline product isolated in 86% yield turned out to be a mixture of at least two stereoisomeric compounds 174, trimers of the 8,9-diazadispiro[2.0.2.4]deca-7,9-diene (173) evidently formed via the normal [4 + 2]-cycloadduct 172 after nitrogen extrusion (Scheme 25) [13b]. 

A reaction which leads to the exclusive or predominant formation of one of the several possible stereoisomeric compounds is called stereoselective reaction. A reaction where a given isomer leads to one product while another stereoisoimer leads to opposite product is called a stereospecific reaction. Let us illustrate this by examples. 

The direction of oxirane ring-opening in the stereoisomeric compounds 289 depends on several factors for example, favored axial attack of the nucleophile, anchimeric assistance of neighboring groups, and conformational control of the approaching nucleophile. The examples shown in Scheme 2 provide support for the importance of each factor. There are, however, exceptions to these rules (see, for example, Ref. 184). Therefore, the results of oxirane ring-opening in 289 cannot always be foreseen. 

Prococcillenine (320) was found in several species of the tribe Coccinelli together with the corresponding N- oxide coccillenine and stereoisomeric compounds. See (77H(7)685) for a review on the structure, synthesis and biosynthesis of ladybug alkaloids. 

On the other hand, most of the lyases allow a reasonably broad variation of the electrophilic acceptor component, which usually is an aldehyde. This feature, which nicely complements the emerging trend of combinatorial synthesis [38-40], makes possible a stereodivergent strategy for the synthesis of groups of stereoisomeric compounds by employing separate enzymatic catalysts to selectively produce individual diastereomers at will from the same starting material (Sect. 7). 

Inversion of configuration at the phosphane phosphorus atom of 3a is most likely due to 3lP NMR spectroscopically monitored dynamic phenomena. Keeping 3a at 60°C for 3 hours leads to an irreversible thermodynamically more stable 4aE. The energy of activation is calculated to 80.5 kJ/mol. According to X-ray structure determinations of 3a and 4aE the SS stereoisomeric compound is subject to a Cope rearrangement, resulting in the EE stereoisomeric form (Scheme 9). 

Many benzofuran-2-ones find application as dyes. For example, styryl analogues based on compound 262 were developed as a polymer colorant <2000W00053597>. Compounds 263 and 264 are among several stereoisomeric compounds that are patented as dyes <2000W00024736>. Dibenzofuran 265 is a photochromic compound for use as an ink or in plastic films <2001CNP1328109>. 

Derivation Two stereoisomeric compounds made by the partial chlorination of acetylene. 

Stereoisomeri — carbon (or phosphorus) atoms that are connected to four different groups will give stereoisomeric compounds that are biologically different from each other... 

The addition of the carbanion from diethyl (3-butenyl)phosphonate to 1-nitroalkenes yields the stereoisomeric compounds (191). ... 

Diastereoisomers are all stereoisomeric compounds which are not enantiomers. In other words, the terminology distereoisomer essentially includes compounds containing both ring systems and double-bonds simultaneously. In apparent contrast to enantiomers diastereoisomers invariably display different physical and chemical characteristics, namely ... 

The formation of the aforementioned compounds proceeds with remarkable selectivity. Only one stereoisomer has been identified for each constitutionally different "mono telomer (14, n = 1), whereas for compounds with n = 2 and = 3, two and four stereoisomeric compounds have been isolated, respectively. It has been assumed that trans addition to 6 is strongly favored under the conditions used. This assumption was substantiated by the small coupling constant (Jvic = 2.0 Hz) that was consistently observed for all telomers. Rigorous proof of the trans stereochemistry comes from the chemical transformations of the telomers. Thus, compounds of the general formula 14 contain protected a-hydroxyaldehyde function, and in principle they should be readily transform-... 

Therefore, we found following thing throughout the synthetic study. 1) We achieved the total synthesis of saponin 2 that was found not to be sweet. This suggests that 2 is not the structure of the natural saponin osladin. 2) We isolated natural osladin from the rhizomes of the fern, P. vulgare. A single crystal X-ray diffraction study of natural osladin shows that it is the stereoisomeric compound 3. Furthermore, osladin is only 500 times sweeter than sucrose. 3) A total synthesis of 3 was achieved and thus the sweet principle of this fern was proved to be osladin. ... 

Prostaglandin Intermediates. Schemes 10.14 through 10.17 outline some synthetic routes to several derivatives of 9 and 10. These stereoisomeric compounds... 

The four stereoisomeric compounds represented by (437) have been prepared. trans-isomers, on buffered ethanolysis, yielded (438) and (439) separately and quantitatively. The cis-isomers gave mainly olefin and acetates. 

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