Abstract: New process for preparing the pheromone active compound lineatin (3,3,7-trimethyl-2,9-dioxatricyclo[3,3,1,0.sup.4,7 ]-nonane), by reacting a 2,2-dimethyl-3,4-pentadienal of formula 1, in which R.sub.1 and R.sub.2 is each hydrogen or lower alkyl, with .beta.-methylallyl magnesium halide; the formed 2,5,5-trimethylocta-1,6,7-trien-4-ol derivative of formula 2 is subjected to oxidation which does not attack the double bonds; the formed 2,5,5-trimethylocta-1,6,7-trien-4-one derivative of formula 3 is subjected to pyrolysis; the formed 1,4,4-trimethyl-6-methylenebicyclo[3,2,0]heptan-3-one derivative of formula 4 is subjected to oxidation; the resulting 5,5,9-trimethyl-2,6-dioxa-7-oxo-bicyclo[4,2,0]octylspiro[2,7]-decane derivative of formula 5 is subjected to oxidation; the resulting 1,5,5-trimethyl-4-oxabicyclo[4,2,0]-octan-3,7-dione of formula 6 is reduced in a per se known manner to lineatin of formula 7. Compounds 2, 3, 4 and 5 are novel.