Cyclic ethers with 5- to 7-membered rings are formed by sulphenoetherification of unsaturated alcohols with N-(pheny1thio)morpholine and trifluoromethanesulphonic acid. ... Whilst the exact nature of episulphonium (and episeleno- nium) ions remains controversia1,l there is no doubt that these intermediates are most useful in organic synthesis. Particu- larly notable are cyclization reactions in which an internal tion' nucleophile (Scheme is captured, l).2,3 such as ...
