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Absolute asymmetric...
Absolute asymmetric synthesis of stereochemically labile aldehyde helicates and subsequent chirality transfer reactions.
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- Johansson, Anna, 1977 (author)
- Gothenburg University,Göteborgs universitet,Institutionen för kemi,Department of Chemistry
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- Håkansson, Mikael, 1957 (author)
- Gothenburg University,Göteborgs universitet,Institutionen för kemi,Department of Chemistry
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(creator_code:org_t)
- Wiley, 2005
- 2005
- English.
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In: Chemistry (Weinheim an der Bergstrasse, Germany). - : Wiley. - 0947-6539. ; 11:18, s. 5238-48
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Abstract
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- Helical complexes formed between aluminum tris(2,6-diphenylphenoxide) (ATPH) and five different aldehydes have been prepared and structurally characterized by X-ray diffraction. It was found that [Al(OC6H3Ph2)3PhCHO] (2), [Al(OC6H3Ph2)3(4-CH3C6H4CHO)] (3), [Al(OC6H3Ph2)3(4-tBuC6H4CHO)] (4), and [Al(OC6H3Ph2)3(p-CH3OC6H4CHO)] (5) all crystallize as conglomerates, while crystals of [Al(OC6H3Ph2)3(o-CH3OC6H4CHO)] (6) are racemic. Supramolecular CH/pi interactions between molecules in crystals of 2-5 that enable stereochemical information to be mediated in three dimensions have been identified and explain the high frequency of conglomerate formation among ATPH helicates. Since 2-5 are stereochemically labile and thus enantiomerize rapidly in solution, the conglomerates can be resolved by crystallization-induced asymmetric transformation. The determination of the enantiomeric excess (ee) in solid samples of stereochemically labile molecules is not trivial, but solid-state CD spectroscopic data, anomalous dispersion data, and the ee values in alkylation reactions all indicate that preferential crystallization of 2-5 yields an essentially enantiopure product. Thus the preparation of 2-5 constitute new examples of absolute asymmetric synthesis. The helical chirality can be transferred (and thus trapped) to alcohols (with ee values of up to 16%) in crystal-to-crystal reactions with achiral organometallic reagents.
Subject headings
- NATURVETENSKAP -- Kemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences (hsv//eng)
Publication and Content Type
- ref (subject category)
- art (subject category)
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