AbstractThe thermolysis of 1,1′‐disubstituted dicyclopropyl ethers with substituents AcO, OH (3a); MeO, OH (3b) and HO, OH (3c) has been studied, together with the sulfide 3d, the thioether analogue of 3c. It is found that the cyclopropyl ethers 3 easily split off cyclopropanone, which cannot be isolated as such because of rapid oligomerisation. This is accompanied by some ring‐opening to a 2‐hydroxyallyl cation, CH2C(OH)\documentclass{article}\pagestyle{empty}\begin{document}$\rm{C}^\oplus $\end{document}CH2, thus explaining the ultimate formation of substituted acetones. No evidence for the transient existence of O‐protonated cyclopropanone magnified image, isomeric with the hydroxyallyl cation, could be obtained. The sulfide 3d behaves entirely differently: on heating it gives the spirocyclic sulfur compounds 12 and 13. The formation of these products is explained in terms of d‐orbital participation of sulfur in the stabilisation of an intermediate cyclo‐propylsulfinium ion.