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Substituent effects in the enantioselective reduction of acetophenones with nabh 4 in the presence of β‐cyclodextrin
Author(s) -
Deratani André,
Renard Estelle
Publication year - 1994
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.530060810
Subject(s) - chemistry , acetophenone , substituent , steric effects , enantiomer , cyclodextrin , selectivity , hydrogen bond , enantioselective synthesis , alcohol , aqueous solution , medicinal chemistry , stereochemistry , organic chemistry , molecule , catalysis
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, CH 3 , NO 2 , OCH 3 ) with aqueous NaBH 4 . 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.