Reaction of 2,3‐dichloro‐1,4‐naphthoquinone with dithiooxamide. Synthesis of dibenzo[b,i]thianthrene‐5,7,12,14‐tetrone

The reaction of 2,3‐dihalogeno‐1,4‐naphthoquinone with dithiooxamide gave dibenzo[b,i]thianthrene‐5,7,12,14‐tetrone in high yield but not 2,2′‐bis(naphtho[2,3‐d]thiazole‐4,9‐dione) which was previously reported. A similar reaction of 3,4‐dichloro‐N‐phenylmaleimide with dithiooxamide also gave the corresponding sulfur heterocycles but not the reported bisthiazole.