Synthesis of polycyclic nitrogen‐containing heterocyclic : One pot formation of 1,6‐naphthyridine ring system by reaction of amino‐cyano‐methylthio‐heterocycles with dialkyl acetyeledicarboxylates

Reaction of 3‐amino‐3‐methylthio‐2‐cyanoacrylonitrile (1) with excess dimethyl acetylenedi‐carboxylate(DMAD) in the presence of potassium carbonate in dimethyl sulfoxide gave a novel tricyclic heterocycle, hexamethyl l H ‐1,4,7‐triazaphenalene‐2,3,5,6,8,9‐hexacarboxylate ( 5a ). When one equivalent of DMAD was used in this reaction, dimethyl 4‐amino‐3‐cyano‐2‐methylthiopyridine‐5,6‐dicarboxylate ( 3a ), a key intermediate of 5a , was obtained.