Reinvestigation of Base-Catalyzed Condensation of Ethyl α,α-Dichloroacetoacetate with Aldehydes. A New Synthesis of (±)-Disparlure

The titled reaction gave ethyl 2-chloro-2,3-epoxyalkanoates (2) and ethyl 3-chloro-2-oxoalkanoates in improved yields. The structure of the by-product was revised as 1,5-dichloro-4,8-dialkyltricyclo[5.1.0.03,5]octane-2,6-dione by means of the 13C–1H two-dimensional NMR spectrum and an X-ray crystallographic analysis. Compound 2 was applied to the synthesis of (±)-disparlure, the pheromone of the gypsy moth, in 49% overall yield via 6 steps.