Recent applications of microwave assisted cyclizations promoted by polyphosphoric acid esters to the synthesis of nitrogen heterocycles

Abstract

Polyphosphoric acid (PPA) esters PPE (ethyl polyphosphate) and PPSE (trimethylsilyl polyphosphate) are mild reagents of the Lewis acid type with a high dehydrating power due to their ability to react irreversibly with water.They are used mainly to conduct condensation reactions in which they bond to the oxygen atom present in alcohols, carbonyls and carboxylic acid derivatives generating electrophilic carbon species.The introduction describes the preparation, structure and applications of PPE and PPSE in the construction of heterocyclic moieties by both C-C and C-heteroatom bond formation. The main body of this chapter is devoted to the applications of the reagents to the synthesis of nitrogen heterocycles under microwave irradiation developed by our group.