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Asymmetric Syntheses of 3-Deoxy-3-aminosphingoid Bases: Approaches Based on Parallel Kinetic Resolution and Double Asymmetric Induction
- Csatayová, Kristína, Davies, Stephen G., Fletcher, Ai M., Fowler, Thomas R., Kennedy, Matthew S., Roberts, Paul M., Thomson, James E.
- Journal of organic chemistry 2017 v.82 no.23 pp. 12447-12466
- diastereoselectivity, enantiomers, esters, lithium, organic chemistry, oxidation, serine
- The asymmetric syntheses of a range of N- and O-protected 3-deoxy-3-aminosphingoid bases have been achieved using two complementary approaches. dl-Serine was converted to a racemic N,N-dibenzyl-protected γ-amino-α,β-unsaturated ester which was resolved using a parallel kinetic resolution (PKR) strategy upon reaction with a pseudoenantiomeric mixture of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide and lithium (S)-N-3,4-dimethoxybenzyl-N-(α-methylbenzyl)amide, giving the corresponding enantio- and diastereoisomerically pure β,γ-diamino esters. Alternatively, elaboration of l-serine gave the corresponding enantiopure N,N-dibenzyl-protected γ-amino-α,β-unsaturated ester, and doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide was found to proceed under the dominant stereocontrol of the lithium amide reagent in both cases, thus augmenting the accessible range of β,γ-diamino esters. Both of these protocols were expanded to include in situ oxidation of the enolate formed upon conjugate addition, giving access to the corresponding α-hydroxy-β,γ-diamino esters. Elaboration of these β,γ-diamino and α-hydroxy-β,γ-diamino esters gave the protected forms of the 3-deoxy-3-aminosphingoid base targets.