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Chiral 2‐Aryl‐2‐methyl‐2 H ‐1‐benzopyrans: Synthesis, characterization of enantiomers, and barriers to thermal racemization
Author(s) -
Harié Guenäelle,
Samat André,
Guglielmetti Robert,
van Parys Inge,
Saeyens Wim,
de Keukeleire Denis,
Lorenz Klaus,
Mannschreck Albrecht
Publication year - 1997
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19970800409
Subject(s) - racemization , chemistry , enantiomer , aryl , circular dichroism , optical rotation , ring (chemistry) , organic chemistry , stereochemistry , alkyl
The ease of thermal breaking of the C(sp 3 )O bond of the 2‐aryl‐2‐methyl‐2 H ‐1‐benzopyrans 1 – 9 was evaluated by measuring the free energy (Δ G e ≠ ) of the racemization reaction of optically active compounds. The variation of Δ G e ≠of the thermal ring opening in terms of structural modifications is discussed. The synthesis of the studied compounds, the preparative separation of enantiomers by liquid chromatography, the determination of enantiomeric purity, the circular dichroism of enriched enantiomers, and the measurement of rate constants of enantiomerization by monitoring the decrease of the polarimetric angle of rotation at suitable temperatures are described.