Acid-catalyzed transannular cyclization of medium ring unsaturated sulfides. The effect of ring size and double bond geometry on rate

Abstract

The acid-catalyzed transannular cyclization of 8–10-membered γ,δ-unsaturated cyclic sulfides yields cis fused bicyclic sulfonium salts independently of the geometry of the double bond. The rate varies linearly with the acidity function –(H₀)_I with a slope of 1. The rate variations span about six powers of ten range, the maximum rate difference being observed for the E/Z thiacyclooct-4-ene pair. The data are consistent with the classical interpretation of the intramolecular reactivity in terms of internal strain of the substrate and/or of the transition state.