Reaction of 1,4-dichlorobut-Z-yne with inorganic sulphides produces 1 , 6-dithiacyclodeca-3,8-diyne (11) which undergoes base-catalysed rearrangement to the bicyclic thiophen, 4,9-dithiabicyclo[5,3,O]deca-l, (10) ,2,7-triene THE properties of the Huckel-type hydrocarbon, [lS]ann~lene,~ prompted an attempt to synthesise the iso-x-electronic 1,6,1 l-trithiacyclopentadeca-2,4,7,9,12,1i-hexaene. An obvious starting material for this compound is the isomeric triacetylene 1,6,1 l-trithiacyclopentadeca-3,8,13-triyne (I), and the reaction between 1,4-dichlorobut-2-yne and sodium sulphide was explored in the hope that (I) would be at least one of the products formed. In the event much polymer was encountered but a crystalline high-melting sparingly-soluble product was isolated in low yield (much improved by use of ammonium sulphide) with the expected empirical formula C,H,S. A conventional molecular-weight determination was precluded by the low solubility of the compound. However, massspectrometry measurements showed no peak higher than a mass number of 167 corresponding to a molecular ion, C8H,S2+ of a cyclic diacetylene, C,H,S2 of structure (11). This indication was fully confirmed by X-ray crystallography. The crystal was found to be monoclinic with lattice parameters a = 7-38, b = 4.44, c = 13-25 A, p = 109" 30', space group PZ,/c. The sharpened Patterson projection on (010) was interpreted by a superposition m e t h ~d , ~ and gave a direct determination of the molecuIar structure. There are two molecules in the unit cell and as there are four equivalent positions in the space group PZJc the molecule is required to be centrosymmetric; thus it cannot possess a boat-like conformation but must be either flat or, much more probably, chair-like (IIa). The atomic co-ordinates were refined by several cycles of structure-factor and Fourier
