The base catalysed reaction of carbon disulphide with the active methylene groups of chloropyridines 4 and 7, followed by alkylation with reagents which also contain active methylene groups, lead to ketene dithioacetals. Further reaction with base afforded highly substituted thiophenes.
Sturrock, K. R., Bremner, D. H., & Wishart, G. (2011). The preparation of ketene dithioacetals and thiophenes from chloropyridines containing an active methylene group. Heterocycles, 82(2), 1657 - 1662. https://doi.org/10.3987/COM-10-S(E)59