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The rate of methyl transfer to pyridine-d5 of δ-ammoniomethylsulfurane, i.e., S,N-dimethyl-6,7-dihydro-5H-dibenzo [b,g][1,5] thiazocinium salt ( 1 ), was slower by 1300 times than that of methyldiphenylsulfonium salt ( 3 ). Activation parameters at 25 °C were obtained for 1 ,ΔH≠=23.1,ΔS≠=−7.8, and for 3 ,ΔH≠=18.1 kcal/mol,ΔS≠=−10.3 e.u., which are in accord with the hypervalent bonding of 1 .