Formation of cyclic sulfonium salts by Me(3)SiI-promoted intramolecular displacement of hydroxide or methoxide by sulfide. Ring contraction thiepane->thiolane

A suitably positioned (1,2-, 1,4-, and 1,5-) intramolecular sulfide interferes with the iodotrimethylsilane-promoted iodine for hydroxyl substitution, as well as the related alcohol deprotection procedure (regioselective cleavage of methyl ethers). The outcome may be a cyclic sulfonium salt or an iodide arising from cleavage of a sulfonium intermediate. Cyclization is especially favored with secondary and tertiary alcohols or ethers, and with an aliphatic more than an aromatic sulfide function. A transannular version of the reaction results in the facile ring contraction of a 7- to a 5-membered cyclic sulfide. Copyright (C) 1996 Elsevier Science Ltd