Hydroxymethyl-BEDT-TTF is converted by tosylation and elimination into exo-methylene-BEDT-TTF whose exocyclic double bond leads to a small increase in the oxidation potential, and from which radical cation salts with perchlorate and triiodide have been prepared, the latter showing semiconductor properties. Allyloxymethyl- and allylthiomethyl-BEDT-TTF, the first BEDT-TTF derivatives with an alkene in the side chain, have been prepared, along with a 1 : 2 radical cation perchlorate salt of the former, an insulator which contains a donor dication.