Ugi-derived dehydroalanines as a pivotal template in the diversity oriented synthesis of aza-polyheterocycles

Divergent Synthesis of Pentacyclic Isoindolinones Enabled by Sequential Insertion of Two Different Isocyanides and Acid Promoted Cyclization of Ketenimines

A palladium-catalyzed multicomponent reaction involving o-bromobenzaldehydes and two different isocyanides was developed to assemble series of isoindolinones with spiroindolenine or azepinoindole skeletons. This sequential insertion reaction features mild conditions, a wide substrate scope, and high efficiency. Preliminary mechanistic study indicated that the difference in steric hindrance between isocyanide components is crucial when regulating the reaction sequence, whereas the ligand also played an important role during the whole process.

Synthesis of Lactams via Isocyanide-Based Multicomponent Reactions

Lactams are very important heterocycles as a result of their presence in a wide range of bioactive molecules, natural products and drugs, and also due their utility as versatile synthetic intermediates. Due to these reasons, numerous efforts have focused on the development of effective and efficient methods for their synthesis. Compared to conventional two-component reactions, multicomponent reactions (MCRs), particularly isocyanide-based MCRs, are widely used for the synthesis of a range of small heterocycles including lactam analogues. Despite their numerous applications in almost every field of chemistry, as yet there is no dedicated review on isocyanide-based multicomponent reactions (IMCRs) concerning the synthesis of lactams. Therefore, this review presents strategies towards the synthesis of α-, β-, γ-, δ- and ε-lactams using IMCRs or IMCRs/post-transformation reactions reported in the literature between 2000 and 2020.

1 Introduction

2 Developments in Lactam Synthesis

2.1 α-Lactams

2.2 β-Lactams

2.3 γ-Lactams

2.3.1 General γ-Lactams

2.3.2 Benzo-Fused γ-Lactams

2.3.3 Spiro γ-Lactams

2.3.4 α,β-Unsaturated γ-Lactams

2.3.5 Polycyclic Fused γ-Lactams

2.4 δ-Lactams

2.5 ε-Lactams

3 Conclusions

Catalyst-Free One-Pot Synthesis of Densely Substituted Pyrazole-Pyrazines as Anti-Colorectal Cancer Agents

The first catalyst-free post-Ugi cascade methodology was developed for expeditious access to structurally diverse and complex pyrazole-pyrazines in one-pot. This novel cascade reaction features an intramolecular N2-arylation of pyrazoles with allenes at the C-β position of triple bond. Screening in the colorectal cancer cell lines HCT116 and SW620 validated the feasibility of the methodology for generating bioactive compounds. The lead compound 7h which is active against HCT116 and SW620 with IC₅₀ of 1.3 and 1.8 µM, respectively, can be synthesized and purified in a gram process synthetic scale in 7 hours. The mechanical studies indicated that compound 7h can induce cell cycle arrest in the G2/M phase and inhibit proliferation and viability in human colon cancer cells. Overall, compound 7h is represented as a promising starting point for the development of new anti-colorectal cancer drugs.

Combination of multicomponent KA2 and Pauson-Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

The Cu-catalyzed multicomponent ketone–amine–alkyne (KA²) reaction was combined with a Pauson–Khand cycloaddition to give access of unprecedented constrained spirocyclic pyrrolocyclopentenone derivatives following a DOS couple-pair approach. The polyfunctional molecular scaffolds were tested on the cyclopentenone reactivity to further expand the skeletal diversity, demonstrating the utility of this combined approach in generating novel spiro compounds as starting material for the generation of chemical libraries. The chemoinformatics characterization of the newly-synthesized molecules gave evidence about structural and physicochemical properties with respect to a set of blockbuster drugs, and showed that such scaffolds are drug-like but more spherical and three-dimensional in character than the drugs.

A concise and unexpected one-pot methodology for the synthesis of pyrazinone-fused pyridones

A post-Ugi/Michael/Retro-Michael reaction, aromatization and 5-exo-dig cyclization cascade reaction was developed and utilized for the synthesis of pyrazinone-fused pyridone derivatives under mild reaction conditions in one-pot.

Diversity-Oriented Synthesis of Highly Fluorescent Fused Isoquinolines for Specific Subcellular Localization

A multicomponent diversity-oriented synthesis of new highly emissive tetracyclic isoquinolines that target specific organelles is described. The title compounds were prepared via a three-step protocol starting with an Ugi four-component reaction, followed by either an intramolecular alkyne hydroarylation and subsequent alkene isomerization or through a Pomeranz-Fritsch-type cyclization with a final intramolecular Heck reaction. Subcellular localization studies of these compounds using green channel confocal microscopy revealed remarkable and distinctive distribution patterns in live cells, showing an unprecedented high selectivity and imaging contrast. The differentiated organelle visualization-including localizers for mitochondria, lysosomes, Golgi apparatus, endoplasmic reticulum, and plasma membrane-was achieved by varying the nature of the tetracyclic system and substituent pattern, changing the original four-component set in the starting Ugi reaction.

Dehydroamino acids: chemical multi-tools for late-stage diversification

α,β-Dehydroamino acids (dhAAs) are noncanonical amino acids that are found in a wide array of natural products and can be easily installed into peptides and proteins. dhAAs exhibit remarkable synthetic flexibility, readily undergoing a number of reactions, such as polar and single-electron additions, transition metal catalyzed cross-couplings, and cycloadditions. Because of the relatively mild conditions required for many of these reactions, dhAAs are increasingly being used as orthogonal chemical handles for late-stage modification of biomolecules. Still, only a fraction of the chemical reactivity of dhAAs has been exploited in such biorthogonal applications. Herein, we provide an overview of the broad spectrum of chemical reactivity of dhAAs, with special emphasis on recent efforts to adapt such transformations for biomolecules such as natural products, peptides, and proteins. We also discuss examples of enzymes from natural product biosynthetic pathways that have been found to catalyze many similar reactions; these enzymes provide mild, regio- and stereoselective, biocatalytic alternatives for future development. We anticipate that the continued investigation of the innate reactivity of dhAAs will furnish a diverse portfolio dhAA-based chemistries for use in chemical biology and drug discovery.

β-Carbolinone Analogues from the Ugi Silver Mine

Here we describe a facile, tandem synthetic route for β-carbolinones, a class of natural products of high biological significance. Commercially available building blocks yield highly diverse analogues in just two simple steps.

Acid-Promoted One-Pot Synthesis of Substituted Furan and 6-Methylpyrazin-2(1 H)-one Derivatives via Allene Intermediate Formed in Situ

Under the acidic conditions, substituted furans were constructed from γ-alkynyl ketones through corresponding allene intermediates in one-pot. The methodology was also tailored to a series of the Ugi reaction products for the synthesis of 6-methylpyrazin-2(1 H)-one derivatives. The current method offered significant advantages for the combinatorial applications of these chemical scaffolds.

Synthesis of Structurally Diverse Emissive Molecular Rotors with Four-Component Ugi Stators

The use of the multicomponent Ugi reaction to rapidly prepare a library of dumbbell-like molecular rotors is highlighted here. The synthetic strategy consisted of the atom-economic access to 15 bulky and structurally diverse iodinated stators, which were cross-coupled to the 1,4-diethynylphenylene rotator. From those experiments, up to six rotors 1a-c and 1l-n were obtained, with yields ranging from 35 to 69% per coupled C-C bond. In addition to the framework diversity, five of these compounds showed aggregate-enhanced emission properties thanks to their conjugated 1,4-bis(phenylethynyl)benzene cores, a property that rises by increasing the water fraction (f_w) in their THF solutions. The results highlight the significance of the diversity-oriented synthesis of rapid access to new molecular fluorescent rotors.

Multicomponent access to indolo[3,3a-c]isoquinolin-3,6-diones: formal synthesis of (±)-plicamine

The complete tetracyclic core structure of plicamine, a novel Amaryllidaceae-type alkaloid, was expeditously prepared by an Ugi four-component condensation reaction, followed by a one-pot sequential phenolic oxidation and intramolecular coupling process.

Copper-catalyzed cycloaddition between hydrogen phosphonates and activated alkenes: synthesis of phosphonoisoquinolinediones

A new and general method for the synthesis of phosphonoisoquinolinediones has been achieved through copper-catalyzed phosphonation–cyclization of various methacryloylbenzamides with P(O)H compounds.

Practical synthesis and cytotoxic evaluation of the pyrazino[1,2-b]-isoquinoline ring system

A multicomponent three-step synthesis of pyrazino[1-2b]isoquinolines is described. A preliminary cytotoxic screening against cancer cell lines was performed.