- Controlled racemization and asymmetric transformation of α-substituted carboxylic acids in the melt
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The racemization and asymmetric transformation of a series of α- substituted carboxylic acids, viz. mandelic acid, hydratropic acid, ibuprofen and naproxen, were studied. Several racemization methods for mandelic acid were studied and it was found that base-catalyzed racemization in aprotic polar solvents was the most efficient method. Moreover, a fast and mild base- catalyzed racemization reaction in the melt was developed. DBN turned out to be a very efficient racemizing base for the substrates studied. Combination of the base-catalyzed racemization in the melt with known resolution processes resulted in crystallization-induced asymmetric transformations. Treating racemic ibuprofen or hydratropic acid with 1.5-2.5 equivalents of enantiopure α-methylbenzylamine and a catalytic amount of DBN resulted in the isolation of enantiomerically enriched ibuprofen or hydratropic acid with ees of up to 75% and almost quantitative yields.
- Ebbers, Eelco J.,Ariaans, Gerry J. A.,Bruggink, Alle,Zwanenburg, Binne
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p. 3701 - 3718
(2007/10/03)
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- Asymmetric Induction in the Diels-Alder Reactions of α-Hydroxy Acyl Nitrones
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The hydroxamic acids 7, derived from a series of α-hydroxy acids 5, have been oxidised with periodate to form transient, chiral acyl nitroso compounds 8, which were trapped in situ with cyclopentadiene and cyclohex-1,3-diene to give mixtures of diastereoi
- Kirby, Gordon W.,Nazeer, Muhammad
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p. 1397 - 1402
(2007/10/02)
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- ASYMMETRIC INDUCTION IN THE DIELS-ALDER REACTIONS OF α-HYDROXYACYLNITROSO COMPOUNDS
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Transient, chiral α-hydroxyacylnitroso compounds (2), able to form intramolecular hydrogen bonds, react stereoselectively with cyclopentadiene and cyclohexa-1,3-diene; the cycloadduct (6) of the latter diene and the nitroso derivative of (S)-mandelic acid
- Kirby, Gordon W.,Nazeer, Muhammad
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p. 6173 - 6174
(2007/10/02)
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