Stereochemistry of planarchiral compounds,part XII: Absolute chiralities and X-ray crystal structures of 2,2′-Bi(1,6-methano[10]annulenyl)s |
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Authors: | Axel Meyer Karl Schlögl Walter Keller Christoph Kratky |
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Institution: | (1) Institut für Organische Chemie, Universität Wien, A-1090 Wien, Austria;(2) Institut für Physikalische Chemie, Universität Graz, A-8010 Graz, Austria |
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Abstract: | Summary The absolute chirality of the dextrorotatory main rotamer of 10,10-dibromo-2,2-bi(1,6-methano10]annulenyl) (1 b), obtained by low temperature chromatography or by crystallisation of the (+)-enantiomer of1 b, was established by observation of anomalous X-ray diffraction as (+)-(R)
p
(R)
a
(R)
p
-1b. This result was confirmed by reduction of (+)-1 b to a dextrorotatory 2,2-bi(1,6-methano10]annulenyl) (1 a), which in turn was accessible by coupling of (–)-2-Bromo-1,6-methano10]annulene (3) of known chirality (S)
p
and, moreover, by enantioselective chromatography of1 a on triacetyl cellulose in ethanol. This correlation determines also the chirality of (+)-1 a as (S)
p
(S)
p
.According to the X-ray analyses the main rotamer of (+)-1 b and the meso-form (2 b) adopt crystal structures in which the bromine atoms come close to the CH2-bridges. The torsional angles around the 2,2-bonds vary between 33°, 53° and 65° for (+)-1 b, racem.1 b and the mesoform2 b, respectively.Dedicated to Prof. Dr. G. Snatzke (Bochum) with cordial wishes on the occasion of the 60th anniversary of his birthday |
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Keywords: | Bijvoet method Chemical and chiroptical correlation Circular dichroism Enantioselective chromatography 10 10-Dibromo-2" target="_blank">gif" alt="prime" align="BASELINE" BORDER="0">-Dibromo-2 2-bi(1" target="_blank">gif" alt="prime" align="BASELINE" BORDER="0">-bi(1 6-methano[10]annulenyl) Torsional isomers |
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