Synthesis of fused triazolo-imidazole derivatives by sequential van Leusen/alkyne–azide cycloaddition reactions

Isocyanide-Based Multicomponent Reactions Coupled One-Pot Process: Efficient Tools to Diversity-Oriented Synthesis of Structural Peptidomimetics

Multicomponent diversity-oriented synthesis (DOS) of conformationally anchored structural peptidomimetics like 2,5-diketopiperazines (2,5-DKP) containing heterocyclic bioisosteres of the amide bond, such as 1,2,3-triazoles and 1,5-disubstituted tetrazoles (1,5-DS-T) is described. Structural peptidomimetics are synthesized from similar available starting materials, via a strategy based on isocyanide-based multicomponent reactions (IMCRs): Ugi-4CR and Ugi-Azide (UA), followed by a one-pot process: SN2/intramolecular alkyne-azide cycloaddition (IAAC). The sequential aligning of two powerful synthetic tools (IMCR and IAAC) has parallelly contributed to generate anchored conformation and complexity in target molecules, which are considered structural peptidomimetics of 2,5-DKP. Herein, the 1,2,3-triazole ring plays a key role in the preference for the boat conformation. Furthermore, the use of UA reaction generates scaffold diversity at the N-1 α-carbon of the pyrazinone ring, replacing a linear amide bond with a heterocyclic bioisostere such as 1,5-DS-T leading to the synthesis of novel tricyclic peptidomimetics. The DFT calculations confirmed the boat conformation of the synthesized molecules.

Advances in the Synthesis of Fused 1,2,3-Triazoles via a MCR-Intramolecular Azide-Alkyne Cycloaddition Approach

The present review narrates several reports which deal with the synthesis of fused 1,2,3-triazole containing scaffolds following a sequential multicomponent reaction (MCR)-intramolecular azide-alkyne cycloaddition (IAAC) approach. The reviewed reactions were cleverly designed so as to incorporate azide and alkyne functionalities in the MCR product which was then subjected to IAAC. The review is divided into two sections based on the number of components in the multicomponent reaction. We have aimed at a critical discussion and also have highlighted either advantages or disadvantages of each methodology.

Synthesis of Imidazole-Based Medicinal Molecules Utilizing the van Leusen Imidazole Synthesis

Imidazole and its derivatives are one of the most vital and universal heterocycles in medicinal chemistry. Owing to their special structural features, these compounds exhibit a widespread spectrum of significant pharmacological or biological activities, and are widely researched and applied by pharmaceutical companies for drug discovery. The van Leusen reaction based on tosylmethylisocyanides (TosMICs) is one of the most appropriate strategies to synthetize imidazole-based medicinal molecules, which has been increasingly developed on account of its advantages. In this review, we summarize the recent developments of the chemical synthesis and bioactivity of imidazole-containing medicinal small molecules, utilizing the van Leusen imidazole synthesis from 1977.

Allosteric GABAA Receptor Modulators-A Review on the Most Recent Heterocyclic Chemotypes and Their Synthetic Accessibility

GABAA receptor modulators are structurally almost as diverse as their target protein. A plethora of heterocyclic scaffolds has been described as modulating this extremely important receptor family. Some made it into clinical trials and, even on the market, some were dismissed. This review focuses on the synthetic accessibility and potential for library synthesis of GABAA receptor modulators containing at least one heterocyclic scaffold, which were disclosed within the last 10 years.

One-Pot Synthesis of Triazolobenzodiazepines Through Decarboxylative [3 + 2] Cycloaddition of Nonstabilized Azomethine Ylides and Cu-Free Click Reactions

A one-pot synthesis of triazolobenzodiazepine-containing polycyclic compounds is introduced. The reaction process involves a decarboxylative three-component [3 + 2] cycloaddition of nonstabilized azomethine ylides, N-propargylation, and intramolecular click reactions.

Sequential Ugi reaction/base-induced ring closing/IAAC protocol toward triazolobenzodiazepine-fused diketopiperazines and hydantoins

A practical three-step protocol for the assembly of triazolobenzodiazepine-fused diketopiperazines and hydantoins has been developed. The synthesis of these tetracyclic ring systems was initiated by an Ugi reaction, which brought together all necessary functionalities for further transformations. The Ugi adducts were then subjected to a base-induced ring closing and an intramolecular azide–alkyne cycloaddition reaction in succession to obtain highly fused benzodiazepine frameworks.

Synthesis and Reactivity of Propargylamines in Organic Chemistry

Propargylamines are a versatile class of compounds which find broad application in many fields of chemistry. This review aims to describe the different strategies developed so far for the synthesis of propargylamines and their derivatives as well as to highlight their reactivity and use as building blocks in the synthesis of chemically relevant organic compounds. In the first part of the review, the different synthetic approaches to synthesize propargylamines, such as A³ couplings and C-H functionalization of alkynes, have been described and organized on the basis of the catalysts employed in the syntheses. Both racemic and enantioselective approaches have been reported. In the second part, an overview of the transformations of propargylamines into heterocyclic compounds such as pyrroles, pyridines, thiazoles, and oxazoles, as well as other relevant organic derivatives, is presented.

New protocols to access imidazoles and their ring fused analogues: synthesis from N-propargylamines

Imidazole and its derivatives are privileged N-heterocyclic structures present in various natural products and synthetic pharmaceuticals.

New route to 1,4-oxazepane and 1,4-diazepane derivatives: synthesis from N-propargylamines

N-Propargylamines are one of the most useful and versatile building blocks in organic synthesis that are successfully transformed into many significant N-heterocycles.

An expedient route to highly diversified [1,2,3]triazolo[1,5-a][1,4]benzodiazepines and their evaluation for antimicrobial, antiproliferative and in silico studies

A simple and facile synthesis of a series of diversified [1,2,3]triazolo[1,5-a][1,4]benzodiazepines has been achieved successfully via a one-pot method under milder conditions and evaluated for their biological activity.

Evolution of a strategy for preparing bioactive small molecules by sequential multicomponent assembly processes, cyclizations, and diversification

A strategy for generating diverse collections of small molecules has been developed that features a multicomponent assembly process (MCAP) to efficiently construct a variety of intermediates possessing an aryl aminomethyl subunit. These key compounds are then transformed via selective ring-forming reactions into heterocyclic scaffolds, each of which possesses suitable functional handles for further derivatizations and palladium-catalyzed cross coupling reactions. The modular nature of this approach enables the facile construction of libraries of polycyclic compounds bearing a broad range of substituents and substitution patterns for biological evaluation. Screening of several compound libraries thus produced has revealed a large subset of compounds that exhibit a broad spectrum of medicinally-relevant activities.

Synthesis of triazolo-fused benzoxazepines and benzoxazepinones via Passerini reactions followed by 1,3-dipolar cycloadditions

Azidobenzaldehydes can be used in Passerini three-component condensations to synthesize small collections of triazolo-fused heterocycles in an efficient and combinatorial fashion upon post-condensation azide-alkyne cycloadditions. Triazolo-fused benzoxazepinones were obtained in moderate to good overall yields with a concise two-step protocol. Triazolo-fused benzoxazepines were instead prepared by means of a longer, yet straightforward route comprising a Passerini reaction, hydrolysis of the ester moiety, O-alkylation with propargylic bromides, and 1,3-dipolar cycloaddition.

Facile one-pot assembly of imidazotriazolobenzodiazepines via indium(III)-catalyzed multicomponent reactions

An operationally simple, one-pot multicomponent reaction has been developed for the assembly of 9H-benzo[f]imidazo[1,2-d][1,2,3]triazolo[1,5-a][1,4]diazepines adorned with three diversification points via an atom-economical transformation incorporating α-diketones, o-azidobenzaldehydes, propargylic amines, and ammonium acetate. This process involves tandem InCl3-catalyzed cyclocondensation and intramolecular azide-alkyne 1,3-dipolar cycloaddition reactions; optimization data, substrate scope, and mechanistic insights are discussed.

Microwave-assisted three-component domino reaction: Synthesis of indolodiazepinotriazoles

A microwave-assisted three-component protocol involving N-1 alkylation of 2-alkynylindoles with epichlorohydrin, ring opening of the epoxide with sodium azide, and an intramolecular Huisgen azide-internal alkyne 1,3-dipolar cycloaddition domino sequence has been described. The efficacy of the methodology has been demonstrated by treating various 2-alkynylindoles (aromatic/aliphatic) with epichlorohydrin and sodium azide furnishing annulated tetracyclic indolodiazepinotriazoles in satisfactory yields.

A Van Leusen deprotection-cyclization strategy as a fast entry into two imidazoquinoxaline families

A concise synthesis of two pharmacologically relevant classes of molecules possessing the imidazoquinoxaline core is reported. The protocol involves use of 1,2-phenylenediamines and glyoxylic acid derivatives, namely ethyl glyoxylate or benzylglyoxamide, along with tosylmethylisocyanides in a microwave-assisted Van Leusen three-component condensation. Subsequent unmasking (Boc removal) of an internal amino-nucleophile promotes deprotection and cyclization that take place either spontaneously in a one-pot fashion to give 8 or upon acidic treatment under microwave irradiation after isolation of the imidazole intermediate to give 11. Of note, a tricyclic framework is hence assembled by means of a rapid and straightforward method with a high bond-forming efficiency.

Straightforward assembly of phenylimidazoquinoxalines via a one-pot two-step MCR process

An efficient multicomponent-based methodology providing a new entry into a medicinally important complex heterocyclic core is presented. The strategy is very general and able to endow target compounds with the highest possible number of diversity points. Notably, four new chemical bonds and two aromatic rings are formed in a one-pot fashion.

Synthesis of Diverse Heterocyclic Scaffolds via Tandem Additions to Imine Derivatives and Ring-Forming Reactions

A novel strategy has been developed for the efficient syntheses of diverse arrays of heterocyclic compounds. The key elements of the approach comprise a Mannich-type, multicomponent coupling reaction in which functionalized amines, aromatic aldehydes, acylating agents, and π- and organometallic nucleophiles are combined to generate intermediates that are then further transformed into diverse heterocyclic scaffolds via a variety of cyclization manifolds. Significantly, many of these scaffolds bear functionality that may be exploited by further manipulation to create diverse collections of compounds having substructures found in biologically active natural products and clinically useful drugs. The practical utility of this strategy was exemplified by its application to the first, and extraordinarily concise synthesis of the isopavine alkaloid roelactamine.

Intramolecular azide-alkyne [3 + 2] cycloaddition: versatile route to new heterocyclic structural scaffolds

Investigating the relatively unexplored intramolecular version of the azide-alkyne [3 + 2] cycloaddition, the present studies demonstrate the utility of the above reaction in the synthesis of a variety of as yet unreported heterocyclic structural scaffolds. The approach involved initial installation of strategic azide and alkyne moieties on a common structural framework, followed by their intramolecular cycloaddition studies. The pivotal azidoalkyne intermediates were efficiently accessed from a variety of easily available starting materials such as olefins, epoxides, amino acids, amino alcohols, ketones etc. The key reactions for incorporation of the azide functionality into the desired framework involved azidolysis of epoxides, displacement of hydroxy groups with azide nucleophiles, and diazo transfer on amine. Attachment of the desired alkyne functionalities was accomplished by either N-, or, O-alkylation with appropriate propargylic halides. The azidoalkynes thus prepared underwent smooth intramolecular cycloaddition, resulting in a variety of novel triazolooxazine and triazolopyrazine derivatives. Interestingly, unlike in the intermolecular version, metal catalysis was not necessary for the performance of the above cycloadditions. It is expected that the results from the present studies and its further extension will provide a potentially fertile pathway to a variety of unique chemical entities of structural and biological significance.

Applications of multicomponent reactions to the synthesis of diverse heterocyclic scaffolds

The sequencing of multicomponent reactions (MCRs) and subsequent cyclization reactions is a powerful stratagem for the rapid synthesis of diverse heterocyclic scaffolds. The optimal MCR is sufficiently flexible that it can be employed to generate adducts bearing a variety of functional groups that may then be selectively paired to enable different cyclization manifolds, thereby leading to a diverse collection of products. The growing interest in diversity-oriented synthesis has led to increased attention to this paradigm for library synthesis, which has inspired many advances in the design and implementation of MCRs for the construction of diverse heterocyclic scaffolds.