Absolute configurations and CD spectra of axially chiral biphenyls prepared in a facile manner by crystallization-induced configuration transformation.
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 DeltaG(#) = 21.45 kcal/mol and the half-life in ethanol at 301 K was 17.1 h.
Wang
Limin
L
College of Pharmaceutical Science and Technology, Tianjin University, Tianjin, People's Republic of China.
Cheng
Senxiang
S
Chen
Rongfeng
R
Chang
Junbiao
J
D000605:Amino Alcohols / Q000737:chemistry; D001713:Biphenyl Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D002942:Circular Dichroism; D003460:Crystallization; D018360:Crystallography, X-Ray; D055620:Optical Phenomena; D013237:Stereoisomerism
D000605:Amino Alcohols; D001713:Biphenyl Compounds