DIASTEREOSELECTIVE AND ENANTIOSELECTIVE ROUTES TO SOME 2,8-DIMETHYL-1,7-DIOXASPIRO[5.5]UNDECANOLS - ABSOLUTE STEREOCHEMISTRY OF (E,E,E)-2,8-DIMETHYL-1,7-DIOXASPIRO[5.5]UNDECAN-3-OL AND OF ((E,E)-8-METHYL-1,7-DIOXASPIRO[5.5]UNDECAN-2-YL)METHANOL PRESENT IN BACTROCERA-CUCUMIS

Routes to the four regioisomeric 2,8-dimethyl-1,7-dioxaspiro[5.5]undecanols have been developed, and in the racemic series, mercury(II)-mediated reactions of appropriate dienone, hydroxy enone, dienedione, and hydroxy dienone systems have been exploited. Most of the epimeric pairs of alcohols (i.e. axial or equatorial) in the E,E, E,Z, or Z,E spiroacetal ring systems have been characterized by detailed H-1, C-13, and correlated NMR spectroscopy and mass spectrometry. Key enantiomers of these alcohols have been obtained by elaborating chiral starting materials such as D-mannitol, L-arabinose, poly(hydroxybutyrate), and in the case of the 5-hydroxy derivative, mandelonitrile lyase mediated formation of a key chiral cyanohydrin was employed. Most of the alcohols, as their trifluoroacetates, are resolved (into enantiomers) on a Lipodex A GC column, thus facilitating their identification from natural sources. In this way, the absolute configurations of a number of 2,8-dimethyl-1,7-dioxaspiro[5.5]undecanols present in the rectal gland secretion of Bactrocera cucumis (cucumber fly) have been determined.