Chiral compounds adamantanes

Chiral separations are concerned with separating molecules that can exist as nonsupetimposable mirror images. Examples of these types of molecules, called enantiomers or optical isomers are illustrated in Figure 1. Although chirahty is often associated with compounds containing a tetrahedral carbon with four different substituents, other atoms, such as phosphoms or sulfur, may also be chiral. In addition, molecules containing a center of asymmetry, such as hexahehcene, tetrasubstituted adamantanes, and substituted aHenes or molecules with hindered rotation, such as some 2,2 disubstituted binaphthyls, may also be chiral. Compounds exhibiting a center of asymmetry are called atropisomers. An extensive review of stereochemistry may be found under Pharmaceuticals, Chiral. 

In an attempt to improve the opacity of the light-scattering state, various additives have been tried [7] such as spherical molecules (e.g., adamantane), ortho-isomers of the usual para-substituted compounds, and chiral compounds [32, 33, 37],... 

Transannular interactions lead to ring closures and reductions to adamantane compounds when dienes of the bicyclo[3.3.1]nonane family are treated with Brpnsted acids and triethylsilane. Compounds 48-51 form reaction mixtures containing various amounts of products 52-54 (R = OH, O2CCF3, Cl) under such conditions.243 The best yields of hydrocarbon 52 occur when the dienes are treated with a 25% excess of sulfuric acid and a 50% excess of triethylsilane in dichloromethane at 20°.243 The stereospecific nature of these transannular reductions is demonstrated by the observation that the enantiomeric purity of the chiral diene 55 is retained in the chiral hydrocarbon product 56 (Eq. 98).243 Dienes of... 

For an adamantane-type compound, it is possible to substitute the four tertiary hydrogen atoms and make four quaternary carbon atoms. These carbon atoms can be asymmetric if the four substituents are chosen properly. It is possible to specify these chiral centers separately, but their chiralities can also be so interlinked that they collectively produce one pair of enantiomers with only one chiral center. Usually it is more convenient to collectively specify the chirality with reference to a center of chirality taken as the unoccupied centroid of the adamantane frame. 

Chirality about an axis is exemplified by allenes, such as the 2,3-penta-diene enantiomer 23. In 23 the methyl and hydrogen substituents on C2 lie in a plane (in the page) that is perpendicular to the plane containing the methyl and hydrogen substituents on C4. Here the axis of chirality is coincident with the C2—C3—C4 bond axis. The structure has a C2 symmetry element, so it is dissymmetric, not asymmetric. The C2 rotation axis is perpendicular to the axis of chirality, as illustrated in Figure 2.13. It must be emphasized that not all structures that are chiral about an axis have a C2 rotation axis. For example, the 2,3-hexadiene enantiomer 24 also has an axis of chirality coincident with the C2-C3-C4 bond axis, but it does not have a C2 rotation axis. The adamantane 25 and appropriately substituted spiro compounds, such as 26, are also chiral about an axis. ... 

Using a model of twistane, identify the cyclohexane ring systems held in twist conformations. In adamantane, find the chair conformation cyclohexane systems. How many are present Evaluate the torsional and angle strain in adamantane. Which of the three compounds in this exercise are chiral ... 

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