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DOI: 10.1055/sos-SD-210-00242

Wessjohann, L. A.; Kaluđerović, G. N.; Neves Filho, R. A. W.; Morejon, M. C.; Lemanski, G.; Ziegler, T.Science of Synthesis: Multicomponent Reactions, (20141415.

General Introduction

The Ugi reaction is the archetypal and arguably also the most frequently used multicomponent reaction, although it is not the oldest one. It can be seen as a variation of the Passerini reaction, in which the oxo component is substituted by an in situ formed imine or rather iminium salt. However, it rapidly became the hallmark of multicomponent reactions because it produces a (usually mono-N-alkylated) dipeptide, i.e. a peptoid-like backbone, found not only in peptides but also in many alkaloids and other heterocycles of biological importance. Another boom in application started when combinatorial and parallel synthesis became in vogue. Beyond its value in combinatorial, heterocyclic, and medicinal chemistry, the Ugi reaction in recent times gained increased acceptance because it can be considered environmentally friendly (water is the only formal byproduct), and is very easy to perform in almost any solvent (with methanol and ethanol being most frequently used, but fluorinated alcohols often being best), or even without solvent.[‌1‌] It allows the rapid and predictable combination of four building blocks, even in the presence of water and air, if the reagents permit. Furthermore, the reaction is unusually insensitive to steric interference, rendering it ideal to generate otherwise difficult-to-reach crowded peptide moieties. For the same reason, however, it also resists most efforts to develop enantioselective or even diastereoselective versions. Several reviews and books cover almost all aspects of Ugi-type multicomponent reactions.[‌2‌‌6‌]

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