Catalysts

Research

Jump to: Review

18 pages, 2562 KiB

Open AccessEditor’s ChoiceArticle

Synthesis, Stereochemical and Photophysical Properties of Functionalized Thiahelicenes

by Valentina Pelliccioli, Francesca Cardano, Giacomo Renno, Francesca Vasile, Claudia Graiff, Giuseppe Mazzeo, Andrea Fin, Giovanna Longhi, Sergio Abbate, Alessia Rosetti, Claudio Villani, Guido Viscardi, Emanuela Licandro and Silvia Cauteruccio

Catalysts 2022, 12(4), 366; https://doi.org/10.3390/catal12040366 - 23 Mar 2022

Cited by 4 | Viewed by 2591

Abstract

We report on the synthesis of a novel class of functionalized thia[6]helicenes and a thia[5]helicene, containing a benzothiophene unit and a second heteroatom embedded in the helix (i.e., nitrogen and oxygen) or a pyrene or a spirobifluorene moiety. These systems are obtained through [...] Read more.

We report on the synthesis of a novel class of functionalized thia[6]helicenes and a thia[5]helicene, containing a benzothiophene unit and a second heteroatom embedded in the helix (i.e., nitrogen and oxygen) or a pyrene or a spirobifluorene moiety. These systems are obtained through straightforward and general procedures that involve: (i) palladium-catalyzed annulation of iodo-atropoisomers with internal alkynes and (ii) Suzuki coupling of iodo-atropoisomers with phenyl boronic acid followed by a Mallory-type reaction. Both experimental and theoretical studies on the configurational stability of some selected thia[6]helicenes confirmed their stability toward racemization at room temperature, while the pyrene-based thia[5]helicene was found to be unstable. Moreover, the configuration assignment for one representative thiahelicene was established through the comparison between experimental and theoretical circular dichroism (CD) spectra. A systematic study of the photophysical properties of both thiahelicenes and the corresponding atropoisomers has been carried out to provide a complete overview on the new molecules proposed in this work. The obtained data showed regular trends in all the thiahelicene series with spectroscopic traits in line with those previously observed for similar heterohelicenes. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Figure 1

8 pages, 2327 KiB

Open AccessArticle

Highly Efficient and Ambient-Temperature Synthesis of Benzimidazoles via Co(III)/Co(II)-Mediated Redox Catalysis

by Renyuan Zhong, Wulin Xiong, Haoyuan Zhang, Tongtong Zeng, Shanshan Gong and Qi Sun

Catalysts 2022, 12(1), 59; https://doi.org/10.3390/catal12010059 - 05 Jan 2022

Cited by 2 | Viewed by 1746

Abstract

An efficient method for ambient-temperature synthesis of a variety of 2-substituted and 1,2-disubstituted benzimidazoles from aldehyde and phenylenediamine substrates has been developed by utilizing Co(III)/Co(II)-mediated redox catalysis. The combination of only 1 mol% of Co(acac)₂ and stoichiometric amount of hydrogen peroxide provides [...] Read more.

An efficient method for ambient-temperature synthesis of a variety of 2-substituted and 1,2-disubstituted benzimidazoles from aldehyde and phenylenediamine substrates has been developed by utilizing Co(III)/Co(II)-mediated redox catalysis. The combination of only 1 mol% of Co(acac)₂ and stoichiometric amount of hydrogen peroxide provides a fast, green, and mild access to a diversity of benzimidazoles under solvent-free conditions. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Graphical abstract

12 pages, 1688 KiB

Open AccessArticle

Acidic Stabilization of the Dual-Aromatic Heterocyclic Anions

by Chongyang Li, Yongli Huang, Chang Q Sun and Lei Zhang

Catalysts 2021, 11(7), 766; https://doi.org/10.3390/catal11070766 - 24 Jun 2021

Cited by 3 | Viewed by 1804

Abstract

Recently, we discovered that the delocalization of nitrogen lone-pair electrons (NLPEs) in five-membered nitrogen heterocycles created a second σ-aromaticity in addition to the prototypical π-aromaticity. Such dual-aromatic compounds, such as the pentazole anion, were proved to have distinct chemistry in comparison to traditional [...] Read more.

Recently, we discovered that the delocalization of nitrogen lone-pair electrons (NLPEs) in five-membered nitrogen heterocycles created a second σ-aromaticity in addition to the prototypical π-aromaticity. Such dual-aromatic compounds, such as the pentazole anion, were proved to have distinct chemistry in comparison to traditional π-aromatics, such as benzene, and were surprisingly unstable, susceptible to electrophilic attack, and relatively difficult to obtain. The dual-aromatics are basic in nature, but prefer not to be protonated when confronting more than three hydronium/ammonium ions, which violates common sense understanding of acid−base neutralization for a reason that is unclear. Here, we carried out 63 test simulations to explore the stability and reactivity of three basic heterocycle anions (pentazole anion N₅¯, tetrazole anion N₄C₁H₁¯, and 1,2,4-triazole anion N₃C₂H₂¯) in four types of solvents (acidic ions, H₃O⁺ and NH₄⁺, polar organics, THF, and neutral organics, benzene) with different acidities and concentrations. By quantum mechanical calculations of the electron density, atomistic structure, interatomic interactions, molecular orbital, magnetic shielding, and energetics, we confirmed the presence of dual aromaticity in the heterocyclic anions, and discovered their reactivity to be a competition between their basicity and dual aromaticity. Interestingly, when the acidic ions H₃O⁺/NH₄⁺ are three times more in number than the basic heterocyclic anions, the anions turn to violate acid−base neutralization and remain unprotonated, and the surrounding acidic ions start to show a significant stabilization effect on the studied heterocyclic anions. This work brings new knowledge to nitrogen aromatics and the finding is expected to be adaptable for other pnictogen five-membered ring systems. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Figure 1

8 pages, 20136 KiB

Open AccessFeature PaperArticle

Tandem Olefin Metathesis/α-Ketohydroxylation Revisited

by Michał Patrzałek, Aleksandra Zasada, Anna Kajetanowicz and Karol Grela

Catalysts 2021, 11(6), 719; https://doi.org/10.3390/catal11060719 - 09 Jun 2021

Viewed by 2089

Abstract

EWG-activated and polar quaternary ammonium salt-tagged ruthenium metathesis catalysts have been applied in a two-step one-pot metathesis-oxidation process leading to functionalized α-hydroxyketones (acyloins). In this assisted tandem process, the metathesis catalyst is used first to promote ring-closing metathesis (RCM) and cross-metathesis (CM) steps, [...] Read more.

EWG-activated and polar quaternary ammonium salt-tagged ruthenium metathesis catalysts have been applied in a two-step one-pot metathesis-oxidation process leading to functionalized α-hydroxyketones (acyloins). In this assisted tandem process, the metathesis catalyst is used first to promote ring-closing metathesis (RCM) and cross-metathesis (CM) steps, then upon the action of Oxone™ converts into an oxidation catalyst able to transform the newly formed olefinic product into acyloin under mild conditions. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Graphical abstract

23 pages, 2997 KiB

Open AccessArticle

Production of 5-Hydroxymethylfurfural from Direct Conversion of Cellulose Using Heteropolyacid/Nb₂O₅ as Catalyst

by Jéssica Siqueira Mancilha Nogueira, Vinícius Tomaz Santana, Paulo Vitor Henrique, Leandro Gonçalves de Aguiar, João Paulo Alves Silva, Solange I. Mussatto and Livia Melo Carneiro

Catalysts 2020, 10(12), 1417; https://doi.org/10.3390/catal10121417 - 04 Dec 2020

Cited by 12 | Viewed by 2794

Abstract

This study aimed to select the best reaction conditions to produce 5-hydroxymethylfurfural (HMF) from cellulose using heterogeneous catalyst based on a heteropolyacid (H₃PW₁₂O₄₀—HPW) and Nb₂O₅. Initially, the influence of the temperature (160 or [...] Read more.

This study aimed to select the best reaction conditions to produce 5-hydroxymethylfurfural (HMF) from cellulose using heterogeneous catalyst based on a heteropolyacid (H₃PW₁₂O₄₀—HPW) and Nb₂O₅. Initially, the influence of the temperature (160 or 200 °C), acetone:water ratio (50:50 or 75:25 v/v), cellulose load (5% or 10% w/v) and catalyst concentration (1% or 5% w/v) on HMF production from cellulose was evaluated through a Taguchi’s L₁₆ screening experimental design. Afterwards, the main variables affecting this process, namely the temperature (160–240 °C) and acetone:water ratio (60:40–90:10 v/v), were optimized using a central composite rotatable design. Next, a kinetic study on HMF production from cellulose was carried out. Finally, HMF production from cellulose obtained from different biomass sources was evaluated. It was found that the reaction conditions able to result in maximum HMF yield, i.e., around 20%, were 200 °C, acetone:water ratio of 75:25 (v/v), 10% w/v of cellulose, and 5% w/v of catalyst concentration. The kinetic study revealed that the Langmuir–Hinshelwood–Hougen–Watson approach fit to the experimental data. Under the optimized conditions, the catalyst HPW/Nb₂O₅ was also effective in converting different sources of cellulose into HMF. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Graphical abstract

8 pages, 1352 KiB

Open AccessArticle

Isoquinolone Synthesis via Zn(OTf)₂-Catalyzed Aerobic Cyclocondensation of 2-(1-Alkynyl)-benzaldehydes with Arylamines

by Dost Muhammad Khan and Ruimao Hua

Catalysts 2020, 10(6), 683; https://doi.org/10.3390/catal10060683 - 17 Jun 2020

Cited by 11 | Viewed by 3220

Abstract

A zinc(II) triflate-catalyzed cyclocondensation of ortho-alkynylbenzaldehydes with arylamines in the presence of base under an oxygen atmosphere affording isoquinolones in good to high yields has been developed. The advantages of the present catalyst system include the use of an air-stable and cheap [...] Read more.

A zinc(II) triflate-catalyzed cyclocondensation of ortho-alkynylbenzaldehydes with arylamines in the presence of base under an oxygen atmosphere affording isoquinolones in good to high yields has been developed. The advantages of the present catalyst system include the use of an air-stable and cheap commercially available Lewis acid as the catalyst, high atom utilization and easily available starting materials. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Graphical abstract

Review

Jump to: Research

79 pages, 17263 KiB

Open AccessFeature PaperReview

Supported Metal Catalysts for the Synthesis of N-Heterocycles

by Laura Antonella Aronica and Gianluigi Albano

Catalysts 2022, 12(1), 68; https://doi.org/10.3390/catal12010068 - 09 Jan 2022

Cited by 13 | Viewed by 4158

Abstract

Nitrogen-containing heterocycles are important scaffolds for a large number of compounds with biological, pharmaceutical, industrial and optoelectronic applications. A wide range of different methodologies for the preparation of N-heterocycles are based on metal-catalyzed cyclization of suitable substrates. Due to the growing interest [...] Read more.

Nitrogen-containing heterocycles are important scaffolds for a large number of compounds with biological, pharmaceutical, industrial and optoelectronic applications. A wide range of different methodologies for the preparation of N-heterocycles are based on metal-catalyzed cyclization of suitable substrates. Due to the growing interest in Green Chemistry criteria over the past two decades, the use of supported metal catalysts in the preparation of N-heterocycles has become a central topic in Organic Chemistry. Here we will give a critical overview of all the solid supported metal catalysts applied in the synthesis of N-heterocycles, following a systematic approach as a function of the type of support: (i) metal catalysts supported on inorganic matrices; (ii) metal catalysts supported on organic matrices; (iii) metal catalysts supported on hybrid inorganic-organic matrices. In particular, we will try to emphasize the effective heterogeneity and recyclability of the described metal catalysts, specifying which studies were carried out in order to evaluate these aspects. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Graphical abstract

25 pages, 3990 KiB

Open AccessFeature PaperReview

DMF as CO Surrogate in Carbonylation Reactions: Principles and Application to the Synthesis of Heterocycles

by Biswajit Panda and Gianluigi Albano

Catalysts 2021, 11(12), 1531; https://doi.org/10.3390/catal11121531 - 16 Dec 2021

Cited by 11 | Viewed by 4818

Abstract

Transition metal-catalyzed carbonylation reactions have emerged as one of the most relevant synthetic approaches for the preparation of carbonyl-containing molecules. The most commonly used protocol for the insertion of a carbonyl moiety is the use of carbon monoxide (CO) but, due to its [...] Read more.

Transition metal-catalyzed carbonylation reactions have emerged as one of the most relevant synthetic approaches for the preparation of carbonyl-containing molecules. The most commonly used protocol for the insertion of a carbonyl moiety is the use of carbon monoxide (CO) but, due to its toxic and explosive nature, this process is not suitable at an industrial scale. More recently, the chemistry of CO surrogates has received large attention as a way to use less expensive and more environmentally friendly methods. Among the various CO surrogates, N,N-dimethylformamide (DMF) has been paid greater attention due to its low cost and easy availability. This mini-review gives appealing insights into the application of DMF as a CO surrogate in metal-catalyzed carbonylations; in particular, in the first part we will give a general state of the art of these reactions for the preparation of carbonyl-containing molecules; then, we will take into account all the various synthetic approaches for the metal-catalyzed carbonylative synthesis of heterocycles using DMF as a CO surrogate. Each protocol has been discussed critically in order to screen the best synthetic method and to offer perspective on trends and future directions in this field. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Graphical abstract

23 pages, 40543 KiB

Open AccessReview

Isoquinolone Syntheses by Annulation Protocols

by Ruimao Hua

Catalysts 2021, 11(5), 620; https://doi.org/10.3390/catal11050620 - 11 May 2021

Cited by 21 | Viewed by 3416

Abstract

Isoquinolones (isoquinolin-1(2H)-ones) are one of the important nitrogen-heterocyclic compounds having versatile biological and physiological activities, and their synthetic methods have been recently developed greatly. This short review illustrates the significant advances in the construction of isoquinolone ring with atom- and step-economy, [...] Read more.

Isoquinolones (isoquinolin-1(2H)-ones) are one of the important nitrogen-heterocyclic compounds having versatile biological and physiological activities, and their synthetic methods have been recently developed greatly. This short review illustrates the significant advances in the construction of isoquinolone ring with atom- and step-economy, focusing on the intermolecular annulation protocols and intramolecular cyclization in the presence of a variety of catalyst systems. The syntheses of isoquinolone-fused rings are also included. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Figure 1

35 pages, 7774 KiB

Open AccessFeature PaperReview

Recent Applications of Heteropolyacids and Related Compounds in Heterocycle Synthesis. Contributions between 2010 and 2020

by Angélica M. Escobar, Guillermo Blustein, Rafael Luque and Gustavo P. Romanelli

Catalysts 2021, 11(2), 291; https://doi.org/10.3390/catal11020291 - 23 Feb 2021

Cited by 14 | Viewed by 4733

Abstract

Over the past two decades, polyoxometalates (POM) have received considerable attention as solid catalysts, due to their unique physicochemical characteristics, since, first, they have very strong Bronsted acidity, approaching the region of a superacid, and second, they are efficient oxidizers that exhibit rapid [...] Read more.

Over the past two decades, polyoxometalates (POM) have received considerable attention as solid catalysts, due to their unique physicochemical characteristics, since, first, they have very strong Bronsted acidity, approaching the region of a superacid, and second, they are efficient oxidizers that exhibit rapid redox transformations under fairly mild conditions. Their structural mobility is also highlighted, since they are complex molecules that can be modified by changing their structure or the elements that compose them to model their size, charge density, redox potentials, acidity, and solubility. Finally, they can be used in substoichiometric amounts and reused without an appreciable loss of catalytic activity, all of which postulate them as versatile, economic and ecological catalysts. Therefore, in 2009, we wrote a review article highlighting the great variety of organic reactions, mainly in the area of the synthesis of bioactive heterocycles in which they can be used, and this new review completes that article with the contributions made in the same area for the period 2010 to 2020. The synthesized heterocycles to be covered include pyrimidines, pyridines, pyrroles, indoles, chromenes, xanthenes, pyrans, azlactones, azoles, diazines, azepines, flavones, and formylchromones, among others. Full article

(This article belongs to the Special Issue Catalysts for the Synthesis of Heterocyclic Compounds)

► Show Figures

Scheme 1

Journal Menu

Journal Browser

Catalysts for the Synthesis of Heterocyclic Compounds

Share This Special Issue

Special Issue Editor

Special Issue Information

Keywords

Published Papers (10 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI