Thia oxa-thia and aza-thia crowns

Abstract The synthesis of macrocyclic thia crown ethers dates back long before the first reports of the synthesis of Pedersen’s oxa crown ethers. Back in 1920, Ray1 reported the synthesis of 1,4,7-trithiacyclononane, 1, which is also known by the acronym [9]-S3, involving reaction of potassium hydrogen sulfide with dibromoethane. In 1934, Meadow and Reid described the isolation of 1,4,7,10,13,16-hexathiacyclooctadecane ([18]-S6), 2, albeit in a yield of 1.7%. It has also been appreciated for some time that in order to avoid undesirable oligomerisations, the co-cyclisation of an acyclic dithiol with an alkyl dihalide should be carried out under conditions of high dilution. Workers at Kodak, for example, described in 1961 the synthesis of [18]-S204, 3, in a 59% yield by working at high dilution in ethanol.