Synthese optisch aktiver 2‐Methyl‐ und 2‐Äthyl‐1, 6‐dioxaspiro [4.4]‐nonan‐ und ‐[4.5]decan‐Pheromone aus einem gemeinsamen chiralen Vorläufer

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.).