Evidence for Intermolecular Interaction between Sulfonium and Sulfide Sulfur Atoms and Its Application to Synthesis of Cyclic Bis(disulfide) Dimer

On the basis of the remote Pummerer reaction of p-bis(alkylthio)-aromatic S-oxides, the intermolecular interaction between the sulfonium and sulfide sulfur atoms is described. (1) In marked contrast to the Pummerer reaction of 1b- d 3 with (CF3CO)2O (J. Org. Chem. 1999, 64, 3190−3195), the reaction of 3,3‘,5,5‘-tetramesityl-4-(trideuteriomethylsulfinyl)-4‘-(methylthio)biphenyl (1a- d 3 ) as a sterically hindered analogue of 1b gave only 2a- d 2 . (2) Both reactions of the two unsymmetrical regioisomers of 1-(ethylthio)-4-(methylthio)benzene S-oxide (5a and 5b) with (CF3CO)2O afforded a mixture of the mono-Pummerer products 6a and 6b, the bis-Pummerer product 7, and the bis-sulfide 8 in a similar ratio. The quenching at the initial stage of both reactions produced 5a, 5b, 8, and the bis-sulfoxide 10 in a similar ratio. These results indicate the equilibrium in the intermolecular interaction between the sulfur atoms. (3) The reaction of the p-bis(benzylthio)-aromatic S-oxide 16 with (CF3SO2)2O gave the cyclic bis(disulfide) dimer 17 for the diphenyl sulfide and diphenylmethane spacers or the cyclic tetrakis(disulfide) tetramer 19 for the benzene and biphenyl spacers via the debenzylation of an intermolecular dithia dication. The cyclic bis(dithia dication) dimer A resulting from the intermolecular interaction between the sulfonium and sulfide sulfur atoms is proposed as an intermediate throughout the present reactions.