Terpenoids—LXX Structure of dehydrocostus lactone

The structure III assigned to dehydrocostus lactone by Sorm et al. has been supported by converting it into (i) guaiane, C₁₅H₂₈ (I) and (ii) s-guaiazulene and chamazulene in fairly high yield from sone of its derivatives. The lactol XII, obtainable from III gives four different products (XIII, XIV, XVIII and XXIV) when subjected to Huang-Minlon reduction at 135° and 170° respectively. The dienic monol (XVIII) the structure of which is supported by UV and NMR spectra, furnished a hydrocarbon C₁₅H₂₆ XXVIII, when subjected to metal amine reduction indicating the presence of an allylic hydroxyl in it, which proves that the lactone attachment in III is at C₆–C₇.