| 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) withaldehydes 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 highlyenantioselective synthesis of 2,2,6-trisubstituted dihydropyrones by the catalytic reaction of diene1 with pyruvates was reported. The isolated intermediates indicated that this asymmetric HDAreaction proceeded in a Mukaiyama aldol pathway. On the basis of the absolute configurations ofthe products, a possible mechanism was proposed. Moreover, the catalytic system could be used tosynthesize a series of enantioenriched β-hydroxyketones 4. Finally, this methodology was successfully applied for the one-step synthesis of the important natural product (R)-(+)-Hepialone with88% isolated yield and 94% enantioselectivity.
|
