SYNTHESIS, CONFORMATION AND TROPICITY OF DIMETHANO-BRIDGED TETRADEHYDROTHIA[21]ANNULENE, TETRADEHYDROTHIA[23]ANNULENE AND TETRADEHYDROTHIA[25]ANNULENE

The title thiaanulenes have been synthesized through a double Wittig r eaction of bis[(triphenylphosphonio)methyl]sulfide dibromide with 6-et hynylcyclohepta-1,3,5-triene-1-carbaldehyde and/or its vinylogous alde hyde, followed by intramolecular oxidative coupling of the resulting b isethynyl sulfides. For each compound, two isomers have been isolated which differed in the geometry of their peripheral olefinic moieties. H-1 NMR spectra revealed that some of the geometrical isomers consiste d of two conformational isomers which differed in the relative disposi tion of the two methane bridges. One isomer for each of the dimethano- bridged thia[21]- and -[23]annulenes sustained ring current, while the other isomers as well as those for the thia[25]annulene did not.