Efficient Synthesis of 3-Substituted Indazoles Using Pd-Catalyzed Intramolecular Amination Reaction of N-Tosylhydrazones

Abstract

The efficient method for the preparation of 3-substituted indazoles was developed using the palladium catalyzed intramolecular amination reaction of 2-bromophenyl hydrazone derivatives. Good functional group compatibility was observed under mild reaction conditions and various 3-substituted indazoles were obtained in moderate to excellent yield.

Base‐Catalyzed Synthesis of Substituted Indazoles under Mild, Transition‐Metal‐Free Conditions

“…Apparently, as hypothesized, some of the E isomer of 1 aa had isomerized to provide additional ( Z )‐ 1 aa , which smoothly underwent cyclization to give 2 a . As known from a study reported by Sakamoto and co‐workers,7d products such as 2 a can be detosylated with magnesium in methanol 20. In this particular case, the transformation provided 1 H ‐indazole 4 in 99 % yield (Scheme ).…”

The efficient synthesis of 3‐[6‐(substituted)‐[1,2,4]triazolo[3,4‐b][1,3,4]thiadiazol‐3‐yl]‐1H‐indazole

“…The frequently used procedures involve chromium tricarbonyl complex, [17] 3-carboxyindazole, [18] trimethylsilylindazole/ CSF, [19] polyphosphoric acid-catalyzed cyclization of 2,6-dihydroxyacetophenone hydrazones, [20] using NaHSO 3 / DMF, [21] palladium-catalyzed intramolecular amination reaction of N-tosyl hydrazones trimethylsilylindazole [22] as well as aryl halides, [23] and copper metal complexcatalyzed synthesis of indazole. [24] Condensation of ofluorobenzaldehydes and their oximes with hydrazine yield indazoles, [25] while 3-substituted indazole and benzoisoxazoles synthesis via palladium catalyzed cyclization reactions [26] indazole N-oxide through 1,7-electrocyclization of azomethine ylides [27] cyclization of o-substituted aryl hydrazones with halogens, nitro and methoxy [28] group as substituent are already reported in the literature. A similar type of simple derivatives is also synthesized by various researchers [29][30][31] using POCl 3 .…”

Transition Metal‐Catalyzed Formation of N‐Heterocycles via Aryl‐ or Vinyl C–H Bond Amination

“…[44] They reported that N-tosylhydrazones 81 could be converted into a range of benzindazoles 82 through palladium(II)-catalyzed oxidative intramolecular arene amination reaction. As with their previous report, the scope of the reaction was broad, tolerating strong electron withdrawing groups (e.g.…”