New syntheses of dillapiol [4,5-dimethoxy-6-(2-propenyl)-1,3-benzodioxole], its 4-methylthio and other analogs

Three syntheses of the natural synergist dillapiol from the natural, commercially available sesamol as starting material, are described. A major difference between these is the order of introduction of the additional methoxy and allyl substituents. In one of the syntheses, a formyl group is introduced at C4 via an electrophilic aromatic substitution reaction and then converted into the methoxy group using a Baeyer-Villiger reaction and subsequent methylation; in the other two, a directed ortho-metalation, Baeyer-Villiger, methylation sequence was employed. Various intermediates along the synthetic route were used to generate more than 30 analogs, including the 4-thiomethyldillapiol, to investigate the structure activity relationships of the pesticide synergism of these compounds. Radio-labeled dillapiol, bearing 14 C at the C4 methoxy group was also prepared. Initial screening with mosquito larvae showed that most of the derivatives prepared in this study had signifacant synergistic activities in combination with the phototoxic larvicide -therthiophene.Key words: dillapiol, insecticide synergists, dillapiol analogs, 4-methylthiodillapiol.