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Helical Phenanthrenes, 3 [1] Syntheses, Enrichment of Enantiomers, and Barriers to Racemization of Twisted 9, 10‐Phenanthrenequinones
Author(s) -
Fritsch Rainer,
Hartmann Erwin,
Andert Doris,
Mannschreck Albrecht
Publication year - 1992
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19921250416
Subject(s) - racemization , chemistry , enantiomer , phenanthrenes , phenanthrene , condensation , medicinal chemistry , organic chemistry , stereochemistry , physics , thermodynamics
The known syntheses of the 9, 10‐phenanthrenequinones 10a – c were improved by the chlorotrimethylsilane modification of the acyloin condensation of biaryl diesters. The novel quinones 4a, 4b , and 12 were prepared. For the first time, enantiomers ( M and P ) of this class of compounds were enriched semipreparatively by liquid chromatography on optically active sorbents. The barriers to thermal racemization amount to 90 – 130 kJ mol ‐1 (Table 2) and are thus higher than the barriers for the corresponding phenanthrene hydrocarbons by roughly 20 kJ mol ‐1 . The reasons for this increase are discussed in terms of repulsive interactions in the transition state of helix inversion.