A convenient non-coupling synthesis of bis(ethylenedithio)tetrathiafulvalene

A new synthesis of bis(ethylenedithio)tetrathiafulvalene (5; BEDT-TTF) has been developed by an unusual route. 4,5-Bis(benzoylthio)-1,3-dithiole-2-thione (1) or commercially available 1,3,4,6-tetrathiapentalene-2,5-dione (2; thiapendione) is directly converted with sodium ethoxide and cis-1,2-dichloroethylene into 1,4,5,8-tetrathianaphthalene (3; TTN; 1,4,5,8-tetrathiatetralin) in high yield. TTN is then tetralithiated with an excess of lithium diisopropylamide in tetrahydrofuran, and sulfur is inserted into the four carbonlithium ion pairs. Subsequent capping on both ends of the reactive intermediate with 1,2-dibromoethane leads to an appreciable yield of BEDT-TTF after recrystallization. The reaction takes advantage of a smooth intramolecular rearrangement of the tetralithiated TTN intermediate. BEDT-TTF is confirmed by 1H-NMR, IR and mass spectroscopy, and is characterized by solution 13C-NMR.