The chemistry of small ring compounds. Part 28: Cyclopropyl cation stabilisation in thermolysis of some cyclopropyl ethers and sulfides

The 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, CH 2 C(OH) {article}{empty}{document}C^⊕{document} CH 2 , 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.