A mixture of 7-formyl-6-(7-hydroxyheptyl)-1,4-dioxaspiro[4,4]nonane [6 g; prepared as hereinbefore described in Example 1(iv)] and hexanoylmethylenetriphenylphosphorane (8.5 g.) in dry tetrahydrofuran (50 ml.) was heated to reflux under nitrogen for 16 hours. The solvent was removed in vacuo and the residue triturated with petroleum ether (b.p. 60°-80° C.), cooled to 0° C. for 1 day, filtered to remove triphenylphosphine oxide and the filtrate evaporated. The residue was again triturated with petroleum ether (b.p. 60°-80° C.) to remove further triphenylphosphine oxide, filtered, and evaporated to give 6-(7-hydroxyheptyl)-7-(3-oxooct-1-enyl)-1,4-dioxaspiro[4,4]nonane (7.5 g.), νmax 1620 cm-1, 1660 cm-1.
