Cycloalkanes, chiral

The enantioselectivities of reactions on chiral surfaces are of interest from a practical standpoint and are the result of enantiospecific differences in reaction energetics and reaction barriers. Another manifestation of the enantiospecific interaction between a chiral adsorbate and a chiral surface is adsorbate orientation. Enantiospecific orientations of chiral adsorbates on naturally chiral metal surfaces have been predicted by molecular simulation studies. The first studies using Monte Carlo methods to study chiral cycloalkanes adsorbed on chiral surfaces pre-... 

One simple test for chirality of substituted cycloalkanes is to represent the ring in planar form. If the planar form is achiral because of a symmetry element, the compound will not... 

Introduction of the allene structure into cycloalkanes such as in 1,2-cyclononadiene (727) provides another approach to chiral cycloalkenes of sufficient enantiomeric stability. Although 127 has to be classified as an axial chiral compound like other C2-allenes it is included in this survey because of its obvious relation to ( )-cyclooctene as also can be seen from chemical correlations vide infra). Racemic 127 was resolved either through diastereomeric platinum complexes 143) or by ring enlargement via the dibromocarbene adduct 128 of optically active (J3)-cyclooctene (see 4.2) with methyllithium 143) — a method already used for the preparation of racemic 127. The first method afforded a product of 44 % enantiomeric purity whereas 127 obtained from ( )-cyclooctene had a rotation [a]D of 170-175°. The chirality of 127 was established by correlation with (+)(S)-( )-cyclooctene which in a stereoselective reaction with dibromocarbene afforded (—)-dibromo-trans-bicyclo[6.1 0]nonane 128) 144). Its absolute stereochemistry was determined by the Thyvoet-method as (1R, 87 ) and served as a key intermediate for the correlation with 727 ring expansion induced... 

Since the ring C s are sp -hybridized, they may be chiral centers. Therefore, substituted cycloalkanes may be geometric isomers as well as being enantiomers or meso compounds. 

Alkanes and cycloalkanes. Obviously a variety of acyclic and cyclic hydrocarbon structures can be synthesized from the appropriate alkyl- or aryl-thiophenes (Scheme 46). The reaction is especially useful for the construction of macrocycles (Scheme 47). One of the most interesting applications of this reaction is in the synthesis of the chiral hydrocarbon butylethylmethylpropylmethane (210) (80JOC2754). The chiral acid (209) was the precursor, in which the thiophene was the potential n-butyl group. Raney nickel desulfurization, followed by standard manipulations to convert the acetic acid unit into an ethyl group, gave the hydrocarbon (210) (Scheme 48) this had [a]578 = -0.198°. It was established that... 

The optically active aryl-methylene cycloalkanes and related compounds, shown in Figure 4, were designed by Schuster et al. as chiral, photobistable materials to be used in particular as chiroptical triggers for the control of liquid crystalline phases (see Section 5.5).[22]... 

Remember In determining chirality in substituted cycloalkanes, always draw the rings as flat polygons. This is especially true for cyclohexane derivatives, where having two chair forms that interconvert can make analysis especially difficult. 

Nemba, R.M. and Balaban, A.T. (1998). Algorithm for the Direct Enumeration of Chiral and Achiral Skeletons of a Homosubstituted Derivative of a Monocyclic Cycloalkane with a Large and Factorizable Ring Size n. J.Chem.InfComput.Sci., 38,1145-1150. 

Klunder, A. J. H., Zhu, J., Zwanenburg, B. The Concept of Transient Chirality in the Stereoselective Synthesis of Functionalized Cycloalkanes Applying the Retro-Diels-Alder Methodology. Chem. Rev. 1999, 99,1163-1190. 

Muller and co-workers [52] have studied the intermolecular rhodium (11) catalyzed C-H insertion of a nitrene derived from [M-(p-nitrobenzenesulfonyl)imi-nojphenyliodinane into cycloalkanes, cycloalkenes, and cyclic ethers. In one example involving indane as the substrate with Pirrimg s chiral phosphate catalyst, the product showed an enantioenrichment of 31% ee, Eq. (34). 

A related but rather special type of substrate is shown in Scheme 16. Achiral cyclo alkyl derivatives such as 38 can be converted to alkylidene-cycloalkanes 40 possessing axial chirality. The reaction of various derivatives 38 (R=f-Bu) and... 

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