Synthesis of Polycyclic Imidazo[1,4]thiazine Derivatives by an ANRORC Domino Reaction

10bH-6-Oxa-1-thia-3a,5-diazaacephenanthrylenes can be easily obtained by a sodium hydrogen carbonate catalyzed anionic domino reaction of thiazolium salts with salicylic aldehydes. It is presumed that the domino sequence includes Krohnke condensation, nucleophilic cyclization, and ANRORC (addition of nucleophile/ring opening/ring closure) steps. To the best of our knowledge, this is a first example of a multistep anionic domino reaction incorporating an ANRORC transformation. The initial generality of the method is demonstrated by using 3-hydroxypyridine-2-carbaldehyde as a carbonyl component.