ChemInform Abstract: Activated Thiocyanates in the Synthesis of Heterocyclic Hansa Yellow Analogues. Synthesis and Colour Measurements of 1-(5′-Imino-4′-phenyl- 4′,5′-dihydro-1′,3′,4′-thiadiazol-2′-yl)-3-(pyrid-2′-yl)amino-1,2,3- trioxopropane 2-Arylhydra