ISSN:
0947-3440
Keywords:
[n.2]Metacyclophanes, hydroxy-
;
Thallium oxidation
;
[n.2]Metacyclophanediquinones
;
anti and syn Conformers
;
Ring inversion
;
Hydrogen bonding, intramolecular
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The title compounds, [n.2]metacyclophanediquinones 6a-f, were prepared by oxidation of the corresponding di-tert-butyldihydroxy[n.2]metacyclophanes 5a-f with Tl(OCOCF3)3 in CF3COOH. When [n.2]quinonophanes 6a-e were reduced with Zn powder in acetic acid, the corresponding tetrahydroxy derivatives 8a-e were obtained, which were converted to the tetraacetates 9a-e. The solution conformations of diquinones 6a-f and tetrahydroxy[n.2]MCPs 8a-e are sensitive to the chain length of the bridges. The ring inversion barriers determined by variable-temperature 1H-NMR spectroscopy decrease with increasing length of the bridges. In addition, a solvent effect on the ratio of anti to syn conformers was found to occur in tetrahydroxy[6.2]metacyclophane 8d and dihydroxy[6.2]metacyclophanes 5d, 10d, and 12d. The conformationally rigid tetraacetoxy[n.2]metacyclophanes 9 exhibit fixed „anti“ and „syn“ conformations. The anti and syn ratio is strongly governed by the number of methylene bridges. Thus, a anti-to-syn ratio of the tetraacetoxy[5.2]- (9c) and -[6.2]metacyclophane (9d) differing from that of the tetraols 8c and 8d was obtained. This difference is due to the ring inversion of 8c and 8d. The assignment of anti and syn conformations was confirmed by 1H-NMR analyses. The dynamics of the ring inversion is also discussed.
Additional Material:
4 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.1995199506141
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