Chemistry of N-(1-haloalkyl)heteroarylium salts

Publisher Summary This chapter discusses N-substituted pyridinium salts that are important synthetic reagents in many fields of organic chemistry. It explores that the first preparation of N-(1-bromo and chloroalkyl)heteroarylium salts using a three-component reaction consisting of an N-heteroaromatic compound such as pyridine (an aldehyde) and thionyl chloride or bromide. This very convenient method has invoked significant current interest in such compounds and has led to many interesting synthetic applications. These salts have been reacted—in many cases in situ —with a variety of nucleophiles. The chapter also reviews systematic investigations that have yielded many useful products such as novel C1-sulfonato-pyridinium betaines, C1-phosphonato-pyridinium salts, geminal-substituted bis-onium salts such as phosphonium/pyridinium species as well as bis-heteroarylium compounds. One can synthesize 5-, 6-, and 7-membered ring systems as well as unusual imines using the title compounds. The most recent applications for these salts are as precursors for the synthesis of novel cationic tricyclic (5/6/5) heterocyclic systems.