Tethered dithiacyclopropenones. Syntheses and structural properties of tetrathiacyclopropenonophanes

The reaction of the cyclic tetrathiadiynes 4(m.n) (where m and n indicate t he number of methylene groups between the dithiaacetylene units) with sodiu m trichloroacetate and subsequent hydrolysis of the gem-dichlorocyclopropen es afforded the mono- and biscyclopropenone derivatives 5(m.n) and 6(m.n) i n moderate yields. Investigation of the X-ray crystal structures revealed s mall torsion angles between the CH2-S bond and the C-C double bond, indicat ing conjugation between the sulfur 3p lone pair and the cyclopropenone ring . The maintenance of the conjugation determines the secondary structure of both (5, 6) ring systems.