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Enamines are key reactive species in many asymmetric organocatalytic reactions. The field of asymmetric catalytic reactions involving an enamine as a reactive intermediate dates back to the seminal work in the 1970s on proline‐mediated intramolecular aldol reaction of triketone reported by Hajos and Parrish at Hoffmann‐La Roche [1] and Eder, Sauer, and Wiechert at Schering AG [2] (Eq. 1.1). In 2000, List, Lerner, and Barbas reported a proline‐mediated intermolecular aldol reaction (Eq. 1.2) [3], in which enamine is a key intermediate. In the same year, MacMillan reported a Diels‐Alder reaction catalyzed by a chiral imidazolidinone via an iminium ion as a reactive intermediate (Eq. 1.3) [4]. In these reactions, small organic molecules catalyze reactions enantioselectively. Since these discoveries, chemistry based on organocatalysts involving an enamine and an iminium ion as an intermediate has developed dramatically [5]. There are several advantages to performing reactions with organocatalysts: (i) exclusion of water and air is not necessary, (ii) the product is free from metal contamination, (iii) most of the organocatalysts are nontoxic, (iv) most reactions do not need low temperature or high temperature, and (v) it is easy to carry out the reaction on a large scale. Given these merits, many catalysts and reactions have been developed. In the previous book of this series published in 2010 [6], progress in the field of organocatalysis is nicely summarized up to 2010. In this chapter, a brief introduction to enamine and iminium ion species will be presented, including work before 2010, and more recent developments in this field will be expanded. Reactions using a combination of organocatalyst and photocatalyst, which have been developed recently, will be described in Chapter 9 of this book.

(1.1)

(1.2)

(1.3)