CAN-PROMOTED AND DDQ-PROMOTED OXIDATION OF ALKENYL SULFIDES

Vinyl sulfides 1 react with CAN in acetonitrile at room temperature to give radical cations 2A in equilibrium with the thiiranyl radical cat ions 2B. The reaction products arise from nucleophilic attack of the n itrate counterion at either the sulfur atom of 2A or the trivalent car bon of 2B. The last reaction can proceed through 1,2-shift or displace ment of the sulfide moiety. When alpha-methylenic protons are present in 2B, deprotonation occurs, leading to allyl radicals and, ultimately , to isomeric allyl alcohols. Reactions of 1 with DDQ in acetonitrile afford charge-transfer complexes and then zwitterionic electron-transf er (ET) complexes which can evolve rapidly through intramolecular prot on transfer when trans methylenic protons are present. The resulting s ulfur-oxygen sigma-complexes are responsible for the reaction products mainly through either gamma-elimination of DDQH(2) or nucleophilic at tack at the delta-vinylic carbon followed by displacement of DDQH(-).