Remote pummerer reaction via intermolecular through-space interaction between sulfonium and sulfenyl sulfur atoms

The remote Pummerer reaction of the mono-sulfoxide of p-bis(methylthio)-aromatic 1 is described. The reaction of 1 with (CF3CO)(2)O in CH2Cl2 gave a mixture of the corresponding mono-Pummerer product 2, the bis-Pummerer product 3, and the bis-sulfide 4 in an n:1:1 ratio (n greater than or equal to 2). The 1:1 formation of 3 and 4 indicates an intermolecular interaction between sulfur atoms. The reaction with the deuterium-labeled 1-d(3) showed that the formation of 2 occurs at the sulfenyl as well as sulfinyl groups in 1a-d(3)-1d-d(3), in which the product ratio of 2-d(3):2-d(2) is in the range of 3.5-10. On the other hand, the Pummerer reaction of 1e-d(3) occurred preferably at the sulfinyl group in a usual manner. The reaction of a 1:1 mixture of the bis-sulfide 4 and the bis-sulfoxide 5 with (CF3-CO)(2)O also gave 2, 3, and 4 in a ratio similar to that for the reaction of 1. The mechanism in the present remote Pummerer reactions is discussed in light of an intermolecular through-space interaction between the sulfonium and sulfenyl sulfur atoms, and a dithia dication dimer B and/or a bis(dithia dication) cyclic dimer C are proposed as intermediates.