| Abstract: | Synthesis of Optically Active 2-Methyl- and 2-Ethyl-1, 6-dioxaspiro 4.4]nonane- and -4.5]decane Pheromones from a Common Chiral Precursor The versatility of the bromoepoxide 6 as chiral building block, which is readily available in both enantiomeric forms from malic acid, and which has previously been used for a vermiculine synthesis, is further demonstrated by the preparation of the title compounds 1, 3, 4 and 5 . Alkylation of 1,3-dithiane, first with the 1-ethoxyethyl-protected ω-chloroalcohols 8b or 9b and then with the (S)-(?)-bromoepoxide 6 , followed by oxirane opening with Selectride or methyl Gilman-reagent creates the desired carbon skeletons and functionality patterns 14–17 , in overall yields of 60–80%. Acetal and thioacetal hydrolyses directly furnish the spiroacetal target structures 1 and 3–5 as 3:2-diastereomeric mixtures; the E/Z-epimers 3 are separated by preparative GC. (Fig.). |
