Preparation and properties of novel sulphur heterocycles from the reaction of 4,5-disubstituted 2-lithio-1,3-dithioles with carbon disulphide and X-ray crystallographic structure of 2-(4,5-dimethyl-1,3-dithiolylidene)-5,6-dimethyl-2,3-dihydro-1,4-dithiine-3- thione

The reaction of 4,5-disubstituted 2-lithio-1,3-dithioles with carbon disulphide followed by treatment with ethyl chloroformate or methyl iodide produces a new type of heterocyclic system. Spectral and analytical data indicated that the molecule consists of a five-membered 1,3-dithiole ring conjugated to an expanded six-membered ring, derived from the former by the insertion of a thiocarbonyl group (9). Single-crystal X-ray diffraction unequivocally identified the 4,5-dimethyl compound (9a):triclinic, P1, with a = 7.852(6), b = 12.253 (22), c = 7.807 (12) Å, α = 78.02 (13), β = 110.29 (10), γ = 91.11 (11)° and Z = 2. The five-membered ring is planar but the six-membered ring is folded. Short intramolecular C=S ⋯ S contacts (3.082 Å) indicate partial bonding between those two sulphur atoms, resulting in a 'no-bond' aromatic system isoelectronic with naphthalene.