A General Method for the Synthesis of Alkylenedithio- and Bis(alkylenedithio)tetraselenafulvalenes

A general synthetic method toward a series of alkylenedithio- and bis(alkylenedithio)tetraselenafulvalenes, i.e., methylenedithio- (MDT-TSF, 1a), ethylenedithio- (EDT-TSF, 1b), propylenedithio-
(PDT-TSF, 1c), bis(methylenedithio)- (BMDT-TSF, 2a), bis(ethylenedithio)- (BETS, 2b), and bis(propylenedithio)tetraselenafulvalene (BPDT-TSF, 2c), as superior electron donors for organic
conductors has been developed. This method is advantageous to ready access to a series of
compounds from common synthetic intermediates, 2-methylthio-3-(2-methoxycarbonylethylthio)-tetraselenafulvalene (6) and 2,6(7‘)-bis(methylthio)-3,7(6‘)-bis(2-methoxycarbonylethylthio)tetraselenafulvalene (7), for the asymmetrical alkylenedithio- and symmetrical bis(alkylenedithio)-TSFs,
respectively. These key intermediates are readily prepared by phosphite-promoted coupling reactions
of 4-methylthio-5-(2-methoxycarbonylethylthio)-1,3-selenole-2-selone (5) or by a reaction of TSF
with LDA and methyl 3-thiocyanatopropionate. The latter method provides not only the successful
conversion of TSF to these heterocycle derivatives but also a generally acceptable route to them,
since TSF is accessible without the toxic and less easily available CSe2.