Chiral cages

The chiral potassium (3)-(+)-2-methyl-l-boraadamantylhydride (.7)-61 - the first chiral cage hydroborate - was prepared as a 0.081 M solution in THF by treatment of (.S ) -58 with potassium hydride. In the nB NMR spectrum of the compound a characteristic doublet at — 18ppm (J111 11 S = 73 Hz) is observed (Scheme 25) <2003MC121, B-2003MI97>. 

Lyotropic polymeric LC, formed by dissolving two aromatic polyamides in concentrated sulphuric acid, have been studied using variable-director 13C NMR experiments.324 The experimental line shapes at different angles w.r.t the external field were used to extract macromolecular order and dynamic in these ordered fluids. An interesting application of lyotropic LC is for the chiral discrimination of R- and S-enantiomers, and has recently been demonstrated by Courtieu and co-workers.325 The idea was to include a chiral compound 1-deutero-l-phenylethanol in a chiral cage (e.g., /1-cyclodextrin) which was dissolved and oriented by the nematic mean field in a cromolyn-water system. Proton-decoupled 2H NMR spectrum clearly showed the quad-rupolar splittings of the R- and S-enantiomers. The technique is applicable to water-soluble solutes. 

The gas-solid addition of HCl or HBr to simple alkylated oxiranes requires their inclusion. (-)-(M)-Tri-o-thymotide (150) (P3i21) selectively enclathrates the oxiranes 151 or 153 with 13-14% ee for (-i-)-(3P)-151 or 51-5Wo ee for (-1-)-(2P,3P)-153. Isolated molecules in the chiral cages of 150 react stereoselectively with HCl or HBr gas to give the products 152 and 154, respectively, in almost stereopure form according to the optical rotations after quantitative reaction under the influence of the chiral environment [78] (Scheme 17). The host lattice is preserved during the reactions, but destroyed during liberation of the product molecules. 

Pieters, R. J. Diederich, F. Enantioselective complexation of excitatory amino acid derivatives by chiral, cage-like C3-symmetrical receptors, Chem. Commun. 1996, 2255-2256. 

Fig. 15 Formation of trigonal prismatic coordination complexes from tripyridine ligand 20 and angular connector 21. Upon guest encapsulation, a dynamic equilibrium between chiral cage 22 and achiral 23 is observed. Reprinted with permission from [75]. Copyright 1999 American Chemical Society...

A variety of chiral alignment media for organic solvents is known with the most widely used and best characterized being the poly(amino acids) PBLG and PCBLL. Both polymers form lyotropic mesophases and possess ot-helical structures for which many examples of enantiomeric differentiation have been shown. In addition to chiral poly(amino acids), it was demonstrated that achiral media with chiral cages like cyclodextrines serve as alignment media with the potential of chiral discrimination.121... 

Chiral cages are such examples of molecules containing several centers of chirality but existing only in two stereoisomeric (enantiomeric) forms the absolute configuration of which can be described according to helicity rules. Thus, the two enantiomers of 4,9-twistadiene are the (lS 3S 6S 8S)-( + )- and (l/ 3/J 6/J 87 )-(—)-isomer,... 

Scheme 1.10. Achiral dimeric aza[70]fullerenes and their chiral cage-opened ketolactam precursors. The third ketolactam (right) is expected to afford a mixture of meso- and d, Z-6,6 -bi-5-aza[70]fullerene.

Figure 11 CD and UV spectra of (6R,15R)-(+)-6,15-dihydro-6,15-ethanonaphtho[2,3-c]pentaphene 3 in dioxane/EtOH and chemical correlation between compound 3 and related compounds, where the most ideal chiral cage compound 3 with two anthracene chromophores shows intense exciton-coupled CD Cotton effects, establishing the consistency between X-ray Bijvoet and CD exciton chirality methods. Redrawn from N. Harada K. Nakanishi, Circular Dichroic Spectroscopy - Exciton Coupling in Organic Stereochemistry, University Science Books Mill Valley, CA, and Oxford University Press Oxford, 1983.

Murakami et al. have reported binding studies on (4Z, 15Z)-bilirubin IXa and pamoic acid with a water-soluble, chiral, cage-type cyclophane (Figure 78)... 

IX. High-Symmetry Chiral Cage-Shaped Molecules.227... 

DC. HIGH-SYMMETRY CHIRAL CAGE-SHAPED MOLECULES... 

C2 symmetry), a high-symmetry chiral cage-shaped tricyclic hydrocarbon closely related to D2 twistane. Wagner-Meerwein rearrangement (144) of the unsaturated carboxylic acid (-)-151 provided the lactone (-)-168, which in turn was converted into the ketone (+)-170 via a series of intermediates, including the mesylate 169 whose intramolecular alkylation was a crucial step in this approach. Removal of the carbonyl group by Wolff-Kishner reduction completed the synthesis of (+)-brexane (171) (145). 

The ability of this chiral cage 5.58 to encapsulte chiral guest molecules such as (15,2/ ,4/ )-(—)-camphorsultam was investigated by NMR spectroscopy, indicating that an encapsulated chiral guest can control the exterior chirality of the assembly 5.58. 

Attention has been mainly focused on the experimental and theoretical aspects of inclusion in chiral cage- and channel-type TOT clathrates, the former manifesting... 

Chiral cage-shaped molecules with high S5rmmetry were reviewed by Naemura, K. in Osawa, E. Yonemitsu, O., Eds. Carbocyclic Cage Compounds Chemistry and Applications VCH Publishers New York, 1992 pp. 61-90. 

Optical resolution of bromochlorofluoro-methane was performed in [131] using its encapsulation by Scheme 2.116 within the cavity of a chiral caging host 184, cryptophane-C, designed to fit substrates of a given size. The diastereo-meric 1 1 cage complex formed by the (-)-mac-robicyclic ligand and the (-)-guest molecule is more stable than those formed by hosts and... 

A chiral caging ligand 278 (Scheme 6.36) is reported [63] to form a supramolecular gyroscope directed toward unidirectional guest rotation. NMR study of rotation of substituted biphenyl guests within the cavity of the capsule showed structure-dependent rotation rate for one of them, the rotation is very slow on NMR time scale at room tanperature [63]. 

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