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Asymmetric synthesis of 3-substituted 3,4-dihydroisocoumarins via stereoselective addition of laterally lithiated chiral 2-(o-tolyl)oxazolines to aldehydes followed by diastereomer-selective lactonization

Authors
Journal
Tetrahedron
0040-4020
Publisher
Elsevier
Publication Date
Volume
61
Issue
13
Identifiers
DOI: 10.1016/j.tet.2005.01.103
Keywords
  • 2-(O-Tolyl)Oxazoline
  • Lateral Lithiation
  • Asymmetric Synthesis
  • 3
  • 4-Dihydroisocoumarin
  • Ab Initio Calculation

Abstract

Abstract Lateral lithiation of ( S)-4-isopropyl-2-( o-tolyl)oxazoline in diethyl ether followed by the reaction with aldehydes in the presence of TMEDA produced the addition products with stereoselectivities up to 84% de. Utilization of TMEDA as a ligand is essential for the good selectivity. Rationale for the stereoselectivity is proposed based on ab initio calculation of the lateral lithio species. The major ( S, S)-products lactonized faster than the minor ( S, R)-products to the corresponding 3,4-dihydroisocoumarins under acidic conditions. Thus, (3 S)-3,4-dihydroisocoumarins were obtained in good optical purities up to 97% ee by sequential application of these matched stereoselective reactions.

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