Methylene Blue As an Additive for Acid-Acid-catalyzed Tandem Reactions Targeting on the Synthesis of Nitrogen-Containing Heterocycles

Methylene blue (MB) was proven to be an effective and amine-compatible additive for helping the establishment of some acid-acid-catalyzed tandem reactions. Addition of MB to acid-catalyzed reaction system not only allowed the use of some basic amines as substrates, which are generally incompatible with the acid conditions, but also enabled the successful synthesis of many important nitrogen-containing heterocycles, such as & beta;-carbolines, pyridines, and quinazolines, in a straightforward manner.