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Absolute configurations and CD spectra of axially chiral biphenyls prepared in a facile manner by crystallization‐induced configuration transformation
Author(s) -
Wang Limin,
Cheng Senxiang,
Chen Rongfeng,
Chang Junbiao
Publication year - 2010
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.20828
Subject(s) - chemistry , axial symmetry , absolute configuration , crystallization , transformation (genetics) , spectral line , crystallography , stereochemistry , organic chemistry , geometry , physics , astronomy , biochemistry , mathematics , gene
Axially chiral biphenyls such as ( M , S )‐ 3k have been conveniently obtained by crystallization of their diastereomeric mixtures, which were synthesized from racemic 4,4′‐dimethoxy‐5,6,5′,6′‐bis(methylenedioxy)‐2‐carboxylester‐2′‐carboxyl‐biphenyls 4 and chiral amino alcohols ( R )‐alaninol, ( S )‐alaninol, ( S )‐valinol, and ( S )‐phenylalaninol. A crystallization‐induced configuration transformation of the biphenyls was thus achieved. It was found that amide formation of an ( S )‐valinol or ( S )‐phenylalaninol at the 2′‐position of the biphenyl usually induced the deposition of crystals with the ( M )‐configuration from ethanol in yields higher than 50%. The absolute configurations (ACs) of two crystalline biphenyls have been determined by X‐ray crystallographic analysis. The ACs of nine biphenyls have been assigned based on their CD spectra. Further, stability investigation of these axially chiral biphenyls revealed that the ACs could revert upon redissolution. The energy barrier to epimerization between ( P , R )‐ 3b and ( M , R )‐ 3b was measured as Δ G # = 21.45 kcal/mol and the half‐life in ethanol at 301 K was 17.1 h. Chirality, 2010. © 2010 Wiley‐Liss, Inc.