ISSN:
0899-0042
Keywords:
host-guest cyclodextrin complexes
;
asymmetric induction
;
solid-state reaction
;
substituent effect
;
steric restrictions
;
hydrophobic interactions
;
hydrogen bonding
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The effect of substituent groups on asymmetric induction by β-cyclodextrin (β-CD) was investigated in the reduction of a series of o-, m-, and p-substituted acetophenones (X = H, Br, Cl, CH3, NO2, OCH3) with aqueous NaBH4. The inclusion of the ketones studied in β-CD led to water-insoluble compounds so that the reaction proceeded in the solid state. The substitutions resulted generally in higher enantioselectivities than that obtained for acetophenone indicating stronger host - guest interactions. Acetophenone and its m- and p-derivatives gave preponderantly the (-)-alcohol while the prevailing enantiomer was the (+)-alcohol in the case of the o-derivatives. The enantioface selectivity was found to be mainly governed by steric demands imposed by the size and the shape of the β-CD cavity in the case of the o-substituted acetophenones and by hydrophobic interactions in the case of the m-derivatives. A more complicated situation arose from the asymmetic reduction of p-derivatives where a combination of these factors with hydrogen bonding of the carbonyl group to the hydroxyls of β-CD are responsible for the enantioselectivity. © 1994 Wiley-Liss, Inc.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chir.530060810
