Synthesis of Polymethinetetrathiafulvalenes by Dimerization of w-(1,3-Dithiol-2-ylidene)polyenals with the Lawesson Reagent: Carotenoid and Supracarotenoid Tetrathiafulvalenes The dimerization of aldehydes via their unstable thioaldehydes giving 1,3-dithietanes, which undergo sulfur extrusion to give alkenes (see Scheme 8) is used for a new, general synthesis of tetrahiafulvalenes with polymethine spacers. In the presence of the Lawesson reagent 19, the 2-(w-oxopolyenylidene)-1,3-dithiol-4,5dicarbonitriles 6 and 13 and the w-(1,3-benzodithiol-2-yliden)polyenals 8 and 15 can be dimerized via the thioaldehydes. The aldehydes 6 and 13 are obtained by reaction of the unsaturated dialdehydes 4, 2,7dimethylocta-2,4,6-trienedial (14a) and crocetindialdehyde (14b) with 1 mol of 2-thioxo-1,3-dithiole-4,5dicarbonitrile (5) and 2 mol of triphenylphosphine (Schemes 5 and 6). The w-(1,3-benzodithiol-2-yliden)polyenales 8 and 15 were prepared by the Wittig reaction of the dialdehydes with 1 mol of (1,3-benzodithiol-(2yl)tributylphosphoniumtetrafluoroborate (12) (Schemes 7 and 6).Starting from the corresponding aldehydes 6 and 13, the polymethinetetrathiafulvalenes 7d, 16a, and 16b with conjugated 16 and 32 polymethine chains become available (Schemes 9 and 10), which we call carotinoid and supracarotinoid tetrathiafulvalenes. The (benzodithiol-2-yliden)acetaldehyde (8a) and -butenal (8b) are dimerized to give the tetrathiafulvalenes 9a and 9b with 4 and 8 methine C-atoms, respectively (Scheme 11). In case of 15a und 15b, the Lawesson method fails, the dimer 17a with 16 methine C-atoms can be obtained from 15a via the McMurry reaction (Scheme 13).The intermediate thioaldehydes can be intercepted by the formation of Diels ± Alder adducts with hexachlorocyclopentadiene and hexa-2,4-diene (Scheme 12). The redox potentials E 1/2 of the described polymethinetetrathiafulvalenes are reported.

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