Synthesis of unsymmetrically substituted TTF derivatives via the 'phosphonate way'. Some investigations on the scope of the method

The scope and limitations of the synthesis of unsymmetrically substituted TTF derivatives via the “phosphonate way” was investigated using as precursors 1,3-dithiol-2-yl-phosphonates and 1,3-dithiol-2-yliden iminium salts with various substitutents on the dithiole cycles. Except for the un- or monosubstituted phosphonates, the one-pot procedure proves to be general and affords in all cases a significant improvement in the overall yields in TTF derivatives. The study has shown also that the formation of the intermediate adducts occurs in high yield, but their transformation into TTF derivatives, in presence of anhydrous acetic acid, is strongly sensitive to the nature of the various substituents, particularly on the iminium part.