Studies on ketene and its derivatives. Part 119. Reactions of haloketenes with 2‐arylideneaminopyridines

Reactions of haloketenes with 2‐arylideneaminopyridines were examined. Reaction of dichloroketene with 2‐benzylideneaminopyridines gave 2,2‐dichloro‐3‐phenyl‐3‐(2‐pyridylamino)propanoic acids and 3‐chloro‐2‐phenylpyrido[1,2‐a]pyrimidin‐4(4H)‐ones. Similar reaction of dichloroketene with 2‐(2‐furfurylideneamino)‐pyridines gave 3‐chloro‐2‐(2‐furyl)pyrido[1,2‐a]pyrimidin‐4‐(4H)‐ones. Chloroketene and chlorophenylketene also reacted with 2‐arylideneaminopyridines to give pyrido[1,2‐a]pyrimidin‐4(4H)‐ones. Ring transformations of pyrido[1,2‐a]pyrimidin‐4‐(4H)‐ones were carried out to give 1,8‐naphthyridin‐4(1H)‐ones and imidazo[1,2‐a]‐pyridines.