Enamines as Synthons in the Synthesis of Heterocycles

Abstract

There is a rich synthetic potential for enamines in heterocyclic synthesis. This chapter reviews the use of enamines as synthons and possible applications of enamines in heterocyclic synthesis. The formation of small rings, five-membered rings, and six-membered rings is also focused in the chapter. In comparison with small-ring heterocycles, the formation of five-membered rings from enamines is quite numerous, with most attention paid to the formation of pyrroles. The synthesis of furan, thiophene derivatives, azoles, and other sulfur as well as phosphorous containing five-membered rings are discussed in the chapter. The synthesis of pyridine derivatives, substituted pyrans, thiopyrans, dioxanes, and seven as well as eight-membered rings are also provided in the chapter. The order of presentation is based on the type of heterocyclic compound formed by these ring-closure reactions. The chapter focuses on the pathways of the cyclization reactions involving enamines and their mechanisms. Enamines can react as electrophiles or nucleophiles and as new partners in cycloaddition reactions. Various derivatives of nitrogen-, oxygen-, and sulfur-containing heterocycles are prepared and these are of interest as starting materials for additional syntheses. They represent potential synthons for the development of various new directions in organic chemistry.