Ugi four-component reactions (U-4CRs) are widely recognized as being highly efficient for the synthesis of pseudopeptides. However, the products of these reactions are not so interesting as drug candidates because they are not conformationally restricted enough for a potent interaction with biological targets. One possible way to overcome this problem is to replace amine and oxo components in the U-4CRs with cyclic imines in so-called Joullié−Ugi three-component reactions (JU-3CRs). This approach provides a robust single-step route to peptide moieties connected to N-heterocyclic motifs that are found as core skeletons in many natural products and pharmaceutical compounds. JU-3CRs also provide much better diastereoselectivity than their four-component analogues. We survey here the redesign of many synthetic routes for the efficient preparation of a wide variety of three-, five-, six-, and seven-membered heterocyclic compounds connected to the peptide backbone. Additionally, in the Ugi reactions based on the cyclic imines, α-acidic isocyanides, or azides can be replaced with normal isocyanides or acids, respectively, leading to the synthesis of N-heterocycles attached to oxazoles or tetrazoles, which are of great pharmaceutical significance. This Review includes all research articles related to Ugi reactions based on the cyclic imines to the year 2020 and will be useful to chemists in designing novel synthetic routes for the synthesis of individual and combinatorial libraries of natural products and drug-like compounds.

A novel bio‐nanocomposite nanocatalyst with highly dispersed particles is synthesized through covalent functionalization of chitosan biopolymer by the multicomponent reaction (MCR) strategy. Surface functionalization of chitosan through MCR is led to the grafting of carboxamide type ligands with a high affinity toward complexation with copper nanoparticles. The catalytic activity of the synthesized catalyst was explored in various transformations such as A3 coupling and click reactions in water. Reusability and non‐hazardous nature of the catalyst, mild reaction conditions, operational simplicity, high yielding, and using water as a solvent are the main advantages of this catalytic protocol.

In the present paper, we report zirconium metal–organic framework (UiO‐66) as an efficient and robust catalyst for the straightforward synthesis of various nitrogen‐containing heterocyclic scaffolds, including imidazopyridine, pyridine and quinoxaline moieties. These compounds with potential drug value which exhibiting a broad spectrum biological and pharmacological activities were successfully accessed with MOF catalytic system under solvent‐free conditions. The main advantage of this protocol is reusability of catalyst, operational simplicity, mild reaction conditions and high‐yielding.

A guanidinium bromide covalently was anchored to a CO2-absorbent metal–organic framework via a two-step postsynthetic modification process and successfully used as a catalyst for the synthesis of cyclic carbonates through cycloaddition of CO2 to epoxides under mild conditions without utilizing any cocatalyst or organic solvent. In this protocol, the synergistic and cooperative effect was anticipated between the catalyst part and the support part to increase the reaction efficiency. Three key factors which are essential for carbon dioxide stabilization reaction were integrated simultaneously in this catalytic system including high CO2 absorption capability of MOF, availability of Lewis acidic centers in MIL-101­(Cr) as a cocatalyst, and presence of guanidinium salt as an efficient catalyst. This method demonstrated a high potential for recycling homogeneous catalysts by maintaining their initial performances.

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