Functionalizable 1H‐Indazoles by Palladium Catalyzed Aza‐Nenitzescu Reaction: Pharmacophores to Donor‐Acceptor Type Multi‐Luminescent Fluorophores

Abstract

Development of small‐molecule‐based multi‐luminescent fluorophores utilizing simple synthetic methodologies, as well as easily available starting materials, has gained much attention in recent years. Herein, we disclose an efficient protocol for the synthesis of N‐protected 1H‐indazole derivatives with diverse substituents at their 3‐ and 5‐positions via palladium‐catalyzed reactions of hydrazones and p‐benzoquinones. The obtained 1H‐indazole derivatives can be easily modified into donor‐acceptor (D−A)‐type chromophores (Indazo‐Fluors) with tunable emission properties in both solid and solution state. Owing to the extent of intramolecular charge transfer, Indazo‐Fluors exhibit positive solvatochromic emission spanning from blue‐green to orange‐red. Theoretical studies were undertaken to rationalize the observed trends in the optical properties of Indazo‐Fluors. Finally, a triethylene glycol (TEG) appended Indazo‐Fluor exhibiting a large Stokes shift and low cytotoxicity allowed us to use it for cell imaging.

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

“…This unusual selectivity in [3 + 2]-cycloadditions of less electron-deficient nitrile imines was studied computationally to rationalize the observed pathways [ 41 ]. Hence, it is worth mentioning that the fused pyrazoles, which are attractive compounds for diverse practical applications in medicinal and materials chemistry, are available not only by the aza-Nenitzescu reaction [ 42 – 43 ] but also via simple and highly efficient [3 + 2]-cycloadditions of nitrile imines with the C=C bond of 1,4-quinones. In general, the present study emphasizes the great importance of nitrile imines as versatile 1,3-dipoles useful for the preparation of N-heterocycles of potential importance for medicinal chemistry, agrochemistry, and materials chemistry [ 44 – 45 ].…”

Synthesis and Photoluminescent Properties of 2-(3-Carboxymethylindazol-1-yl)anilines

“…In addition, a wide range of useful photophysical properties of N-substituted indazoles should be noted. They are used in lighting technology, for light-emitting devices production, as well as in study of biochemical processes in living systems using fl uorescent trackers [10][11][12][13].…”

Metal‐Free Synthesis of Pyrazoles and Chromenopyrazoles from Hydrazones and Acetylenic Esters

“…Hydrazones have been used as an effective substrate for the development of many heterocycles including pyrazoles . We recently reported an efficient method for the synthesis of 5‐hydroxy indazoles from aryl hydrazones and 1,4‐benzoquinones . Subsequently, the strategy was extended towards the synthesis of hybrid polycycles containing a fused indazole and benzofuran unit in one‐pot .…”