Synthesis of unsymmetrically substituted TTF derivatives via the "phosphonate way". Limitations due to the instability of some metalated 1,3-dithiol-2-yl-phosphonates.

The poor results in the syntheses of unsymmetrically substituted TTF deriva tives carried out with mono or unsubstituted diethyl 1,3-dithiol-2-yl-phosp honates is here explained by the existence of an equilibrium between the cy clic and open forms of their corresponding carbanionic salt, with possible dimerisation of the open form. The monomeric cyclic form can react with a h igh reactive iminium salt, affording then the corresponding TTF derivative in moderate yield. (C) 1999 Published by Elsevier Science Ltd. Ail rights r eserved.