title: Partial resolution of racemic trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxyl-2-yl]benzoic acids by the diastereomer method with (R)- or (S)-1-phenylethylamine.
abstract: The partial resolution is described of a series of racemic trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxyl-2-yl]benzoic acids (1), which are the key intermediates for the synthesis of chiral organic radical liquid crystalline compounds and are crystallized to give racemic compounds. Racemic acid 1 [(+/-)-1] with a long alkyl chain (C7 to C13) could be resolved by the conventional diastereomeric salt formation using (R)- or (S)-1-phenylethylamine (2) as the resolving agent, whereas resolution of (+/-)-1 with a short alkyl chain (C4 to C6) was unsuccessful. Use of six equiv of (R)- or (S)-2 for the initial diastereomeric salt formation of (+/-)-1 with a C7-C13 alkyl chain, followed by recrystallization of the resulting salts once or twice, gave 2S,5S- or 2R,5R-enriched 1, respectively, in an ee range of 75-92% and with an overall recovery of 11-27%, based on the original quantity of (+/-)-1.
authors.affiliation: Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Uchida
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Uematsu
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Nakayama
authors.forename: Hiroki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Hirohito
authors.initials: H
authors.lastname: Tsue
authors.forename: Koichi
authors.initials: K
authors.lastname: Tanaka
authors.forename: Rui
authors.initials: R
authors.lastname: Tamura