Libraries of C-5 Substituted Imidazoles and Oxazoles by Sequential Van Leusen (VL)-Suzuki, VL-Heck and VL-Sonogashira in Imidazolium-ILs with Piperidine-Appended-IL as Base

Recent Advances in the Synthesis of Diverse Libraries of Small-Molecule Building Blocks in Ionic Liquids (ILs)

The Account describes recent advances, from the authors’ laboratories, in the synthesis of diverse libraries of small-molecule building blocks employing ionic liquids (ILs). The ability of ILs to act as catalysts/promoters/solvents for electrophilic and onium ion chemistry, as well as in metal-mediated cross-coupling reactions, and the potential to sequence/hyphenate these methods, have opened up new opportunities for facile assembly of functional small molecules with increased complexity from readily available precursors. While Brønsted acidic IL/IL solvent mixtures are suitable media for carbocation and onium ion chemistry, piperidine-appended IL/IL solvent mixtures can successfully catalyze a variety of base-catalyzed reactions. Several widely practiced transformations including ‘name reactions’ were adapted and performed efficiently in ILs.

1 Introduction

2 Aryldiazonium Salts and Aryltriazenes as Coupling Partners in Metal-Mediated C–C Cross-Coupling Reactions in ILs

3 Expanding the Scope of Metal-Mediated Cross-Coupling Reactions in ILs

4 Application of ILs in Synthesis and Functionalization of Hetero­cycles

5 Expanding the Scope of Amide Synthesis in ILs

6 Generation and Chemistry of ‘Tamed’ Propargylic Cations in ILs

7 Newer Nitration Methods for Arenes and Heteroarenes in ILs

8 Halofunctionalization in ILs

9 ‘Name Reactions’and Other Widely Practiced Synthetic Transformations in ILs

9.1 The Biginelli Reaction

9.2 Nitrile Synthesis by the Schmidt Reaction

9.3 Rupe Rearrangement

9.4 Synthesis of 1,3-Dioxanes via Prins Reaction in [BMIM(SO3H)][OTf]

9.5 Synthesis of Cyclopropanes and Oxiranes by the Corey–Chaykovsky (CC) Reaction

10 Conclusions and Closing Remarks

The Use of 5-Hydroxymethylfurfural towards Fine Chemicals: Synthesis and Direct Arylation of 5-HMF-Based Oxazoles

5-Hydroxymethylfurfural (5-HMF) is a renewable platform chemical used as a source for obtaining diverse fine chemicals. In this letter, we report the synthesis of 5-HMF-based oxazole compounds. While 5-HMF could be easily converted into the oxazole derivative through the Van Leusen reaction, the direct arylation step needed to access the final compounds was problematic at first. After optimization, a palladium-catalyzed procedure has been developed and used for the synthesis of a series of 33 derivatives. This article reports an extension of the late-stage CH arylation reaction as an application to the oxazole platform derived from biosourced 5-HMF. The challenges in the preparation of the derivatives containing some electron-withdrawing substituents were overcome by the use of a palladium-free method.

A Facile Microwave-Assisted Synthesis of Oxazoles and Diastereoselective Oxazolines Using Aryl-Aldehydes, p-Toluenesulfonylmethyl Isocyanide under Controlled Basic Conditions

In this study, a highly efficient two-component [3 + 2] cycloaddition reaction of substituted aryl aldehydes with 4-toluenesulfonylmethyl isocyanide (TosMIC) in the presence of 2 equiv of potassium phosphate as a base to 5-substituted oxazoles were established in a isopropanol medium under microwave irradiation. However, using 1 equiv of K3PO4 as a base resulted in the diastereoselective synthesis of 4,5-disubstituted oxazolines under identical reaction conditions. The foremost benefits of these protocols are the moderate-to-excellent yields with good functional group compatibility, simple experimental procedure, inexpensive readily available starting materials, nonchromatographic purification, and high bond-forming efficiency. The synthetic manipulation reported herein represents a cleaner route to the sustainable preparation of 5-substituted oxazoles and diastereoselective 4,5-disubstituted oxazolines derivatives.

Recent Advances in the Synthesis of Oxazole-Based Molecules via van Leusen Oxazole Synthesis

Oxazole compounds, including one nitrogen atom and one oxygen atom in a five-membered heterocyclic ring, are present in various biological activities. Due to binding with a widespread spectrum of receptors and enzymes easily in biological systems through various non-covalent interactions, oxazole-based molecules are becoming a kind of significant heterocyclic nucleus, which have received attention from researchers globally, leading them to synthesize diverse oxazole derivatives. The van Leusen reaction, based on tosylmethylisocyanides (TosMICs), is one of the most appropriate strategies to prepare oxazole-based medicinal compounds. In this review, we summarize the recent advances of the synthesis of oxazole-containing molecules utilizing the van Leusen oxazole synthesis from 1972, aiming to look for potential oxazole-based medicinal compounds, which are valuable information for drug discovery and synthesis.

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.

Palladium-catalyzed Sonogashira coupling reactions in γ-valerolactone-based ionic liquids

It was demonstrated that the γ-valerolactone-based ionic liquid, tetrabutylphosphonium 4-ethoxyvalerate as a partially bio-based solvent can be utilized as alternative reaction medium for copper- and auxiliary base-free Pd-catalyzed Sonogashira coupling reactions of aryl iodides and functionalized acetylenes under mild conditions. Twenty-two cross-coupling products were isolated with good to excellent yields (72–99%) and purity (>98%). These results represent an example which proves that biomass-derived safer solvents can be utilized efficiently in common, industrially important transformations exhibiting higher chemical and environmental efficiency.

Isocyanide-Based Multicomponent Reactions of Free Phenylboronic Acids

Boronic acids are amongst the most useful synthetic intermediates, frequently used by modern drug design. However, their access and fast synthesis of libraries are often problematic. We present a methodology on the synthesis of drug-like scaffolds via IMCRs with unprotected phenylboronic acids. To demonstrate an application of our approach, we also performed one-pot Suzuki couplings on the primary MCR scaffolds. Moreover, we performed a thorough data-mining of the Cambridge Structural Database, revealing interesting geometrical features.