Synthesis of 2H-Indazoles by the [3 + 2] Cycloaddition of Arynes and Sydnones

Abstract

A rapid and efficient synthesis of 2H-indazoles has been developed, which involves the [3+2] dipolar cycloaddition of arynes and sydnones. The process proceeds under mild reaction conditions in good to excellent yields.

Metal Acetylacetonates Covalently Anchored onto Amine Functionalized Silica/Starch Composite for the One-Pot Thioetherification and Synthesis of 2H-Indazoles

“…In heterocyclic chemistry, indazole unit has been recognized as a ''privileged structure'', and is an important pharmacophore in medicinal chemistry [32][33][34][35]. 2H-Indazoles are less studied as compared to 1H-indazoles due to the difficulty in their preparation [36].…”

“…Recently, several promising synthetic routes have been developed for the synthesis of 2H-indazoles, such as palladium-catalyzed intramolecular amination of the corresponding N-aryl-N-(o-bromobenzyl) hydrazines [37]; Fecatalyzed intramolecular N-N bond formation from aryl azides [38]; reaction of highly functionalized zinc reagents with aryldiazonium salts [39]; [3 ? 2] dipolar cycloaddition of arynes and sydnones [33]; reaction of sodium hydride or DBU catalyzed 2-nitrobenzyl triphenylphosphonium bromide with aryl isocyanates [40]; synthesis of 2H-indazoles using Suzuki-Miyaura and Sonogashira couplings [41]. However, most of the existing methods exhibit several drawbacks, such as requirement of additives, low functional group tolerance; and need several steps to synthesize the starting materials.…”

Synthesis of Pyrido[1,2-a]indole Malonates and Amines through Aryne Annulation

“…The ability to expediously synthesize biologically important compounds continues to motivate our labs to explore the full potential of aryne-based methodologies. 15 …”

Acid and base catalyzed Davis–Beirut reaction: experimental and theoretical mechanistic studies and synthesis of novel 3-amino-2H-indazoles

“…1 While the chemistries to and of 1 H -indazoles are well developed, 2 2 H -indazoles are considerably less well studied. 3 In recent years, we have reported the syntheses of a number of pyrazolo-based heterocycles ( 1 ), 2 H -indazoles ( 2 ) and, subsequently, 1 H -indazolones ( 3a/b ) that were obtained via the Davis-Beirut reaction (Figure 1). 4 We previously suggested that o -nitrosobenzylidine was an important intermediate in this chemistry.…”