Unexpected Regioselective Reactions of 2-Bromomethyl-1,3-thiaselenole with Dithiocarbamates: The First Example of Nucleophilic Attack at Selenium Atom of Seleniranium Intermediate

The regio- and stereoselective reaction of 2-bromomethyl-1,3-thiaselenole with sodium N,N-dialkyl dithiocarbamates is accomplished at room temperature for two minutes in MeCN to afford ( Z )-2-{[(dialkylamino)carbothioyl]sulfanylselanyl}ethenyl vinyl sulfides in up to 98% yield. At a longer time (8 h), the reaction regioselectively gives 2,3-dihydro-1,4-thiaselenin-2-yl N,N-dialkylcarbamodithioates in high yields. The latter are formed by rearrangement of the former compounds. DFT calculations show that the reactions proceed via a seleniranium intermediate. The formation of the products is the result of nucleophilic attacks of dithiocarbamate anion either at the selenium atom or at the carbon-2 atom of the seleniranium cation. The reaction leading to sulfanylselanylethenyl vinyl sulfides represents the first example of nucleophilic attack at the selenium atom of seleniranium intermediate.