Synthesis and properties of methanothia-[15]-, -[17]-, -[19]-, -[21]-, -[23]-, -[25]-, -[27]-, -[29]-annulene and dimethanodithia-[26]- and -[30]-annulene

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Double Wittig reactions of the vinylogues of cyclohepta-1,3,5-triene-1,6-dicarbaldehyde with bis[(triphenylphosphonio)methyl] sulphide dibromide afforded the corresponding monomeric and/or dimeric condensation products, i.e. singly methano-bridged thia-annulenes and/or doubly methano-bridged dithia-annulenes; their 1H NMR spectra showed that the methanothia-[17]-, -[19]-, -[23]-, and -[27]-annulene sustain ring current, while the methanothia-[15]-, -[21]-, -[25]-, and -[29]-annulene as well as the dimethanodithia-[26]- and -[30]-annulene do not. Dynamic NMR analysis of the methylene protons revealed the flipping of the methylene bridge above and below the average plane of the macrocycle.