67. The action of halogens on polycyclic indole derivatives. Part IV. Some reactions of 1-keto-1 : 2 : 3 : 4-tetrahydrocarbazole

Synthesis of novel pyrido[3′,2′:5,6]thiopyrano[3,2‐b]indol‐5(6H)‐ones and 6H‐pyrido[3′,2′:5,6]thiopyrano[4,3‐b]quinolines, two new heterocyclic ring systems

“…They were prepared starting from the 2,3-dihydrot h i o p y r a n o [ 2 , 3 -b] p y r i d i n -4 ( 4H) -o n e s 2 a -b [12,13], by known reactions employed in the literature for the obtainment of analogous tetracyclic systems [14][15][16][17][18]. Compounds 2a-b revealed to be versatile intermediates as, recently, they were used for the synthesis of new pyridothiopyrano[4,3-b]indole system 1 [12], which is structurally related to the novel heterocycle A.…”

“…with ethyl formate in anhydrous toluene in the presence of sodium methoxide. Compound 3, containing a methine active group, was able to give the desired 3-phenylhydrazono derivatives 4a, 5a and 6a in particularly good yields, by coupling with the appropriately substituted diazonium salt, by the Japp-Klingemann reaction [14][15][16]. Compounds 4a, 5a and 6a were directly converted to the desired indole derivatives 7 a, 8a a n d 9 a using Fischer cyclization, by reflux in hydrogen chloride ethanolic solution, with yields ranging from 70%-90%.…”