Terpenoids-CIII: synthesis of santanolide 'C', tetrahydroalantalactone, lactone of β-hydroxy eudesman-15-oic acid and (+) dihydrojunenone from eudesmol

Abstract

Dihydroselinene (VII), obtained by the pyrolysis of dihydroeudesmol benzoate (VI) on hydroboration-oxidation yields tetrahydrocostal (VIII, R = CH₂OH). The lead tetraacetate oxidation of VIII gives an oxide (IX) which on purification and oxidation with chromic acid in acetic acid affords santanolide 'C'. By a similar series of reactions 8-β-hydroxyeudesmol (XIV) prepared by LAH reduction of eudesman-8-one (XIII) gives tetrahydroalantalactone (IV) and the lactone of 8-β-hydroxyeudesman-15-oic acid (V), in which the lactone V predominates. The dihydrojunenone mixture (XVI), obtained in our earlier work, on equilibration with alkali followed by extensive chromatography, affords pure dihydrojunenone (XVII). The stereochemistry of the various products has been discussed.