Aryl diazonium salts are versatile building blocks in organic synthesis In light of the ever-increasing importance of aryl diazonium salts spanning most disciplines of the chemical sciences, we review the recent development of aryl diazonium chemistry over the past seven years (2013-2020) Special emphasis is put on various new transformations involving the generation of radical intermediates via thermal, photochemical, and electrochemical means Recent advances in the development of transition metal-catalyzed reactions using aryl diazonium salts are also reviewed Together, these newly developed transformations significantly expand the synthetic chemist's repertoire of aromatic carbon-carbon and carbon-heteroatom bond forming methods using aryl diazonium precursors, providing powerful tools for the synthesis and modification of complex molecular scaffolds

Recent Development of Aryl Diazonium Chemistry for the Derivatization of Aromatic Compounds

Colorimetric and fluorescent probes based on small organic molecules have become important tools in modern biology because they provide dynamic information concerning the localization and quantity of the molecules and ions of interest without the need for genetic engineering of the sample. In the past five years, these probes for ions and molecules have attracted great attention because of their biological, environmental and industrial significance combined with the simplicity and high sensitivity of absorption and fluorescence techniques. Moreover, pyrazole derivatives display a number of remarkable photophysical properties and wide synthetic versatility superior to those of other broadly used scaffolds. This review provides an overview of the recent (2016–2020) findings on chemosensors containing pyrazole derivatives (pyrazoles, pyrazolines and fused pyrazoles). The discussion focuses on the design and physicochemical properties of chemosensors in order to realize their full potential for practical applications in environmental and biological monitoring (sensing of metal ions, anions, explosives, and biomolecules). We also present our conclusions and outlook for the future.

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Recent progress in chemosensors based on pyrazole derivatives

Progress in Photoinduced Radical Reactions using Electron Donor-Acceptor Complexes

Yb(OTf)3-Catalyzed Alkyne-Carbonyl Metathesis-Oxa-Michael Addition Relay for Diastereoselective Synthesis of Functionalized Naphtho[2,1-b]furans.

As one type of chromene, 2H-chromenes represent important oxygen heterocycles, which not only widely exist in natural products, pharmaceutical agents and biologically relevant molecules, but have also been used broadly in materials science and organic synthesis. Two major synthetic strategies have been developed towards such compounds. This review mainly focuses on the recent advances in this field, including benzopyran ring formation involving cyclization reactions and the late-stage functionalization of the parent 2H-chromenes.

Synthesis of 2H-chromenes: recent advances and perspectives.

Highly regioselective organo photocatalysis of 4CzIPN (1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene) for the arylation of 2H-indazole is demonstrated. The present synthetic route provides a highly safe and easily accessible aniline precursor as an arylation reagent. The photoactivated 4CzIPN organocatalyst is found to be more efficient for single electron transfer without any organic base for the radical reaction. The carbazole-based photocatalyst (4CzIPN) with wide redox potential is stable and recyclable for further reaction transformations. Many indazole and aniline derivatives were used in the reaction and provided the arylated indazole derivatives in good to excellent yield.

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Metal-free, regioselective, visible light activation of 4CzIPN for the arylation of 2H-indazole derivatives

Solvent-free and montmorillonite K10-catalyzed domino reactions for the synthesis of pyrazoles with alkynylester as a dual synthon

TfOH mediated easy access to interesting pyrazolines starting from an aldehyde, phenylhydrazine and styrene has been developed. The scope of this synthetic methodology has been explored by synthesizing various 1,3,5-trisubstituted pyrazolines in very good yields with very high regioselectivity. The origin of regioselectivity has been explained by comparing the stability of possible intermediate carbocations. The synthetic utility of a green solvent has been explored by synthesizing some of pyrazolines in a DES medium. The synthetic application of the present methodology is employed in the synthesis of a pyrazoline alkaloid.

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TfOH mediated intermolecular electrocyclization for the synthesis of pyrazolines and its application in alkaloid synthesis

A highly regioselective, carbazole based Electron Donor Acceptor (EDA) catalyzed synthesis of biaryl and aryl–heteroaryl compounds is described. Various indole and carbazole derivatives were screened for the Homolytic Aromatic Substitution (HAS) reaction. Tetrahydrocarbazole (THC) was very efficient for the HAS transformation and proceeded via a complex formation between diazonium salt and electron rich tetrahydrocarbazole. The UV-Vis spectroscopy technique has been used to confirm the complex formation. The in situ generated EDA complex even in a catalytic amount is found to be efficient for the Single Electron Transfer (SET) process without any photoactivation. Biaryl compounds, 2-phenylfuran, 2-phenylthiophene, and 2-phenylpyrrole and bioactive compounds such as dantrolene and canagliflozin have been synthesized in moderate to excellent yields.

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Carbazole based Electron Donor Acceptor (EDA) catalysis for the synthesis of biaryl and aryl-heteroaryl compounds.

1,3,5‐Triphenylpyrazoline‐Based Organocatalysis: Synthesis of Aryl‐Heteroaryl Compounds and Exploiting By‐Product from the Reaction for Alkyne‐Carbonyl Metathesis (ACM) Reaction in One Pot

Sesuraj Babiola Annes

Papers

Metal-free, regioselective, visible light activation of 4CzIPN for the arylation of 2H-indazole derivatives

Solvent-free and montmorillonite K10-catalyzed domino reactions for the synthesis of pyrazoles with alkynylester as a dual synthon

TfOH mediated intermolecular electrocyclization for the synthesis of pyrazolines and its application in alkaloid synthesis

Carbazole based Electron Donor Acceptor (EDA) catalysis for the synthesis of biaryl and aryl-heteroaryl compounds.

1,3,5‐Triphenylpyrazoline‐Based Organocatalysis: Synthesis of Aryl‐Heteroaryl Compounds and Exploiting By‐Product from the Reaction for Alkyne‐Carbonyl Metathesis (ACM) Reaction in One Pot