Probing for Electronic and Steric Effects in the Peracid Oxidation of Thianthrene 5-Oxide

A systematic examination of the electronic and steric effects in the peracid oxidation of thianthrene 5-oxide (SSO) was undertaken and has revealed valuable information on the oxidative reactivity of the SSO mechanistic probe toward peroxidic oxidants. Thus, no significant steric effect was found on the bisulfoxide (SOSO)/sulfone (SSO(2)) product ratio for aliphatic peracids with varying size of alkyl groups [R = Me, Et, i-Pr, t-Bu, (n-Bu)(Et)CHCH(2)]. However, a significant electronic effect was observed for CH(3)CO(3)H and CF(3)CO(3)H, for which the X(SO) values were 0.16 and 0.01, i.e., predominant oxidation of the sulfide functionality to the SOSO product by these oxidants. In addition, substituted perbenzoic acids displayed this trend. In contrast, the nucleophilic peracid anion led exclusively (X(SO) = 1.00) to oxidation of the sulfoxide site to the SSO(2) product. The oxygen transfer appears to be orbital-controlled since the more electrophilic oxidant is clearly the more reactive as well as more chemoselective, i.e., preferred attack at the more nucleophilic sulfide site in SSO.