The cyclization of N-(2-chloropyridin-3-yl)-2-(2-cyanopyridin-3-ylsulfanyl)-N-methylacetamide (I) by mens of K2CO3 in refluxing DMF gives 7-methyl-7,12-dihydro-6H-pyrido[2,3-b]pyrido[2',3':4,5]thieno[2,3-f][1,4]diazepin-6-one (II), which is alkylated with ethyl iodide and NaI in DMF yielding the tetrcyclic ketone (III). Finally, this compound is treated with the sulfirizing agent 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (Lawesson reagent) in refluxing toluene.