ACID-CATALYZED TRANSANNULAR CYCLIZATION OF MEDIUM RING UNSATURATED SULFIDES - THE EFFECT OF RING SIZE AND DOUBLE-BOND GEOMETRY ON RATE

The acid-catalyzed transannular cyclization of 8-10-membered gamma,del ta-unsaturated cyclic sulfides yields cis fused bicyclic sulfonium sal ts independently of the geometry of the double bond. The rate varies l inearly with the acidity function -(H-0)(I) with a slope of 1. The rat e variations span about six powers of ten range, the maximum rate diff erence being observed for the E/Z thiacyclooct-4-ene pair. The data ar e consistent with the classical interpretation of the intramolecular r eactivity in terms of internal strain of the substrate and/or of the t ransition state.