Harnessing Protonated 2,2′-Bipyridinium Salts as Powerful Brønsted Acid Catalysts in Organic Reactions

Abstract

It is the first time that the readily available protonated 2,2′-bipyridinium salts are used as Brønsted acid catalysts to accelerate a series of organic transformations that included the hydration of aromatic alkynes, etherification of alcohols, cyclotrimerization of aliphatic aldehydes, Ritter reaction, Mannich reaction, Biginelli reaction, preparation of substituted alkenes from alcohols, synthesis of spirooxindole, bisindolylmethane, and noncyclized tetraketone with good to excellent yields. These results strongly suggest that there exists enormous potentiality in the development of the protonated 2,2′-bipyridinium catalytic system