A CONVENIENT METHOD FOR THE PREPARATION OF δ-HYDROXY-β-KETOESTERS AND 6-ALKYL-5,6-DIHYDRO-4-HYDROXY-2-PYRONES. APPLICATION TO THE SYNTHESES OF KAWAIN AND DIHYDROKAWAIN

Abstract

Abstract δ-Hydroxy-β-ketoesters[3] and 6-alkyl-5, 6-dihydro–4-hydroxy-2-pyrones[4] were obtained in good yields by TiCl4-promoted addition of diketene[1] to various aldehydes[2], followed by the treatment with alcohol. The hydroxyketoesters[3] were easily lactonized to the corresponding lactones[4] in excellent yields by the hydrolysis with aqueous alkali, followed by acidification. The present method was successfully applied to the syntheses of dihydrokawain[7c] and kawain[7d].