New substrates for the preparation of electroactive materials: The syntheses of chiral tetrathiafulvalene derivatives with hydroxy-functionalised butane-1,4-dithio bridges

The syntheses of two derivatives of TTF containing (2R,3R)-2,3-dihydroxybutane-1,4-dithio bridges is described, for use in the preparation of chiral hydrogen bonded radical cation salts as potentially electroactive materials. The bridges are introduced by reaction of 2-thioxo-1,3-dithiole-4,5-dithiolate with 1,4-disubstituted derivatives of bis-O-protected butane-2,3-diol to give a bicyclic thione. The X-ray crystal structure of the isopropylidene ketal derivative shows that all four sp³ carbon atoms in the eight-membered ring are displaced to the same side of the dithiole plane. Ease of deprotection led to the use of methoxyethoxymethyl (MEM) protecting groups rather than the ketal. Treatment of the bis-MEM-protected bicyclic thione with mercuric acetate and acetic acid led not only to exchange of the exocyclic sulfur for oxygen but also to removal of just one of the MEM groups, which may have wider synthetic applications.