Stereochemistry and mechanism of ionic cyclopropane ring cleavage by arenesulfenyl chloride addenda in quadricyclene systems

Abstract

Addition of benzenesulfenyl chloride to quadricyclenedicarboxylic acid (la) and to the corresponding dimethyl ester (1b) gave adducts [exo-5-chloro-endo-3-phenylthiotricyclo[2.2.1.0^2,6]heptane-2,exo-3-dicarboxylic acid (3a) and the C-3 epimer (4a) from la and the corresponding dimethyl esters from lb, 3b:4b, ca. 1:1]; these are the result of electrophilic cleavage of a cyclopropane ring in this system by retention and inversion processes (in nearly equal amounts). The addition of toluenesulfenyl chloride to lb gives analogous results. All such results demonstrate the lack of bridged sulfonium ions (e.g., 2) as the sole product precursors and indicate that corner-attached electrophilic addition intermediates, relative to the corresponding edge-attached species, may have a far greater importance than previously suspected. The stereochemistry of the adducts was confirmed by spectral (largely proton magnetic resonance) and chemical (lactone formation) studies.