A large number of spiroacetals have been identified in fruit flies of the genus Bactrocera. This thesis describes the enantioselective synthesis of optically active samples of a number of alkyl and/or hydroxy substituted spiroacetals based on the 1,6- dioxaspiro[4.5]decane and l,7-dioxaspiro[5.5]undecane systems.
The synthesis of the E,E, Z,E and E,Z enantiomers of 2-hydroxymethyl-8-methyl-1,7- dioxaspiro[5.5]undecane was achieved from the natural sugars, D-mannitol and L-arabinose. The (2S,5R,6R,8S) and (2R,5R,6S,8R) enantiomers of 2,8-dimethyl-1,7-dioxaspiro[5.5]undecan-5-ols were produced via enzyme catalysed asymmetric addition of HCN to 5-hexenal. The E,E and some Z,E and E,Z enantiomers of the 2,8-dimethyl-1,7- dioxaspiro[5.5]undecan-4-ols, the 2-ethyl-8-methyl-1,7-dioxaspiro-[5.5]undecan-3 and 4-ols, and the 8-ethyl-2-methyl-1,7-dioxaspho[5.5]-undecan-3 and 4-ols were derived from the (R)- and (S)- enantiomers of 1-iodo-3-(tetrahydropyranyloxy)-butane or (R)-1-iodo-3- (tetrahydropyranyloxy)-pentane using alkylative chemistry to provide key hydroxyenones or ketoalcohols which were cyclised by appropriate methods. Detailed spectral analysis including chiral properties were completed to provide the basis for identification and determination of absolute stereochemistry of certain natural spiroacetals.
The 2-hydroxymethyl-1-6-dioxaspiro[4.5]decanes and 3- and 4-hydroxy-1,7- dioxaspiro[5.5]undecanes were synthesised enantioselectively for determination of the absolute configurations of these spiroacetals present in Bactrocera oleae (olive fruit fly), B. cacuminatus and B. distincta. Similarly, the (5S,7S) enantiomer of 7-methyl-1,6- dioxaspiro[4.5]decane was shown to be the natural enantiomer in B. xanthodes by enantioselective synthesis of its antipode.
2-Methyl-6-pentyl-3,4-dihydro-2H-pyran and 2-hydroxy-6-undecanone were identified from B. kraussi and enantioselective synthesis showed these compounds possessed the same chiral sense as the co-ocurring spiroacetals to which these they are probably biosynthetically related.
The determination of the absolute stereochemistry of insect pheromones should provide the basis for a greater understanding of the insects' biochemistry and assist in the development of environmentally acceptable methods of insect control.