Regioselective S-O vs. C-O bond cleavage in sulfenate ester radical anions

The electron transfer (ET) reduction of benzyl benzenesulfenate ester (1) and tert-butyl benzenesulfenate ester (2) was investigated using electrochemical techniques. Analysis of the cyclic voltammetry of each Compound suggests that the ET reduction proceeds via a stepwise dissociative mechanism. The voltammograms of I are similar to those of diaryl disulfides and it was found through controlled potential electrolysis (CPE) product Studies that ET reduction leads to S-O bond cleavage. The voltammograms of 2 are dramatically different with a sharper dissociative wave occurring at a more negative peak potential. CPE experiments indicate products that result from ET leading to C-O bond cleavage in this case. DFT Calculations of the singly occupied molecular orbitals (SOMOs) of 1 and 2 were performed and offer a rationale for the different reactivity of the two radical anions.