Note

Abstract

This work demonstrates that self‐disproportionation of enantiomers via achiral chromatography can be recommended as inexpensive and general method for optical purifica‐ tion of enantiomerically enriched compounds. In particular, the advantage of this approach over conventional recrystallization is that it can be used for both crystalline as well as liquid com‐ pounds. Chirality, 25:365–368, 2013. © 2013 Wiley Periodicals, Inc.

Attracting Enantiomers: Chiral Analytes That Are Simultaneously Shift Reagents Allow Rapid Screening of Enantiomeric Ratios by NMR Spectroscopy

“…In the case of enantioenriched samples, the authors observed two sets of resonances, one for each enantiomer. Dihydroquinoline serves as its own chiral solvating agent (CSA) due to non‐covalent aggregation in solution which is the key requirement for self‐induced diastereomeric anisochronism (SIDA) in NMR spectroscopy and enantioselective self‐disproportionation on achiral phase (ESDA) chromatography …”

“…There is increasing interest in ESDA due to the far‐reaching opportunities related to the separation of enantioenriched mixtures . In addition, the effect is of great interest in enantioselective catalysis with fluorinated substrates and it already serves as a routine test whether unintended change of enantiomeric composition resulted from silica gel chromatography of raw catalysis products …”

Self‐disproportionation of Enantiomers (SDE) of Chiral Nonracemic Amides via Achiral Chromatography

“…For example, SDE via density gradient centrifugation or SDE via sublimation, are far much less known, but can be quite successfully used for practical enantiomeric purifications . Similarly to the distinct crystallographic structures observed in the solid state, chiral compounds in the liquid state or in solution show well‐defined preferences for homochiral/heterochiral dynamic molecular associations, accounting for various nonlinear effects, including SDE via chromatography ,,. Thus, when a solution of a nonracemic compound is subjected to chromatography, such dynamic homochiral/heterochiral molecular associations, having very different chromatographic behaviour, as compared with the corresponding monomers, result in the eluted material of gradually decreasing or increasing variable enantiomeric composition.…”

“…To emphasize the SDE‐phoric property of a trifluoromethyl group, we want to also mention here the results obtained using CF 3 ‐containing amino‐alcohols. SDE experiments performed using amino‐alcohols 7 showed that these compounds have the propensity for a remarkably high SDE magnitude (Figure ) …”

Recent Progress in the in situ Detrifluoro­acetylative Generation of Fluoro Enolates and Their Reactions with Electrophiles

“…Accordingly, in our opinion, the mechanism of these reactions remains unconfirmed and needs additional study. Furthermore, the authors33a,47,48 did not conduct SDE tests49 to verify the reported stereochemical outcome. Nevertheless, highly synthetically interesting products of type 49 can be prepared with good yields and stereoselectivity.…”