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

Abstract

A rapid and efficient synthesis of 2H-indazoles has been developed using a [3 + 2] dipolar cycloaddition of sydnones and arynes. A series of 2H-indazoles have been prepared in good to excellent yields using this protocol, and subsequent Pd-catalyzed coupling reactions can be applied to the halogenated products to generate a structurally diverse library of indazoles.

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

“…The bond between metal and ligand is a lewis acidbase interaction. First, activated silica was converted to silica chloride using thionyl chloride [46], followed by reaction with starch in chloroform and triethylamine to obtain the silica/starch substrate. M(acac) n (where M=Co, Cu, Pd, n = 2; Co, Mn, Ru, n = 3) was refluxed with amine functionalized silica/starch substrate in dry toluene followed by simple filtration and drying in the oven at 110°C.…”

Continuous‐Flow Visible Light Organophotocatalysis for Direct Arylation of 2H‐Indazoles: Fast Access to Drug Molecules

“…An inhibitor of liver X receptor is known to be a key medicine for preventing and treating cardiovascular disease . However, the reported synthetic methods involved tedious steps, drastic conditions and using transition metal‐catalysis . In contrast, both batch and continuous‐flow methodologies developed here were used to synthesize the products 4‐(7‐methoxy‐2‐phenyl‐2 H ‐indazol‐3‐yl)benzonitrile ( 3 w ) and 3‐(4‐chlorophenyl)‐7‐methoxy‐2‐phenyl‐2 H ‐indazole ( 3 x ), with very good yields at room temperature in a single‐step and environmentally benign reaction (Scheme ).…”

Transition-Metal-Free Synthesis of Benzo-Fused Five- and Six-Membered Heterocycles Employing Arynes

“…Larock, Shi, and coworkers have developed a mild method for the synthesis of 2H-indazole derivatives starting from arynes and easily available sydnones through [3 + 2] dipolar cycloaddition/decarboxylation sequence [29,30]. Sydnones are stable mesoionic cyclic compounds.…”

“…A variety of functional groups are tolerated under the reaction conditions, such as ester, nitrile, halo, and amino functionalities. SCHEME 9 Synthesis of 2H-indazoles from arynes and sydnones [29,30]. SCHEME 8 Synthesis of 1H-indazoles from arynes and hydrazones [28].…”