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
✍ Scribed by Yoshiaki Uchida; Toshifumi Uematsu; Yoichi Nakayama; Hiroki Takahashi; Hirohito Tsue; Koichi Tanaka; Rui Tamura
- Book ID
- 102078721
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 152 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0899-0042
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✦ Synopsis
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 2__S__,5__S__‐ or 2__R__,5__R__‐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. Chirality, 2008. © 2007 Wiley‐Liss, Inc.