Highly enantioselective synthesis of 2,6-disubstituted and 2,2,6-trisubstituted dihydropyrones: a one-step synthesis of (R)-(+)-hepialone and its analogues

J Org Chem. 2005 Oct 14;70(21):8533-7. doi: 10.1021/jo051458s.

Abstract

An efficient enantioselective approach to chiral dihydropyrones has been developed by the hetero-Diels-Alder (HDA) reactions of (E)-4-methoxy-2-trimethylsiloxy-penta-1,3-diene (diene 1) with aldehydes and pyruvates. It has been found that the readily accessible (R)-BINOL-Ti(OiPr)(4) (1.1:1) complex was a very effective catalyst for this reaction. Aromatic, heteroaromatic, conjugated, and aliphatic aldehydes afforded the corresponding products in moderate to high isolated yields (up to 99%) with excellent enantioselectivities (up to 99% ee). The first example of highly enantioselective synthesis of 2,2,6-trisubstituted dihydropyrones by the catalytic reaction of diene 1 with pyruvates was reported. The isolated intermediates indicated that this asymmetric HDA reaction proceeded in a Mukaiyama aldol pathway. On the basis of the absolute configurations of the products, a possible mechanism was proposed. Moreover, the catalytic system could be used to synthesize a series of enantioenriched beta-hydroxyketones 4. Finally, this methodology was successfully applied for the one-step synthesis of the important natural product (R)-(+)-Hepialone with 88% isolated yield and 94% enantioselectivity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalysis
  • Molecular Structure
  • Pyrones / chemical synthesis*
  • Pyrones / chemistry
  • Stereoisomerism
  • Structure-Activity Relationship

Substances

  • Pyrones
  • hepialone