Acid-catalysed condensations of 1,5- or 1,6-dicarbonyl compounds with ethylene glycol give 1,3,5-trioxepane derivatives as a result of neighbouring participation by the adjacent carbonyl group during the acetalization process. With trimethylene glycol, the related 1,3,5-trioxocanes have also been obtained. Reaction of the 1,3,5-trioxepanes with (a) Grignard reagents gives dialkyl-substituted cyclic ethers, (b) titanium tetrachloride–allyltributyltin gives diallyl-substituted cyclic ethers and (c) triethylsilane in the presence of trimethylsilyl triflate provides the corresponding cyclic ethers.
