Pyridine cyclodextrin inclusion complexes with

A similar chiral environment is given by inclusion to cyclodextrins (CDs), cyclic oligosaccharides (3). The outside of the host molecule is hydrophilic and the inside hydrophobic. The diameters of the cavities are approximately 6 (a), 7-8 (j3), and 9-10 A (7), respectively. Reduction of some prochiral ketone-j3-CD complexes with sodium boro-hydride in water gives the alcoholic products in modest ee (Scheme 2) (4). On the other hand, uncomplexed ketones are reduced with a crystalline CD complex of borane-pyridine complex dispersed in water to form the secondary alcohols in up to 90% ee, but in moderate chemical yields. Fair to excellent enantioselection has been achieved in gaseous hydrohalogenation or halogenation of a- or /3-CD complexes of crotonic or methacrylic acid. These reactions may seem attractive but currently require the use of stoichiometric amounts of the host CD molecules. 

Electrostatic self-assembly was combined with supramolecular chemistry to obtain inclusion complexes of a polymeric nonlinear optical (NLO) active dye and modified [3-cyclodextrin with induced chromophore orientation [37], The polyanion is a N,N-diallyl-aniline and sodium-2-acrylamido-2-methylpropanesulfonate copolymer functionalized with pendant azo group. The modified /i-cyclodextrin oligo-cation was obtained by treatment of hcptakis(6-dco y-6-iodo-/i-cyclodcxtrin) with excess pyridine. A linear polyamine, chitosan, was also combined with the polyanion, for comparison. Films were deposited on glass slides by dipping them alternatively in aqueous solutions of the cation and the polyanion. UV-visible spectra indicate dye aggregation and suggest the formation of an inclusion complex of the dye with the cyclodextrin, thus isolating the chromophores. 

Reduction of ketones in homogeneous medium in the presence of cyclodex-trins gives disappointing results. However, inclusion of pyridine-borane into ciys-talline P-cyclodextrins generates complexes that reduce prochiral ketones or activated C=C bonds with good enantiomeric excesses [578,579],... 

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