Synthesis of 1-aryl-1H-indazoles via palladium-catalyzed intramolecular amination of aryl halides
| Autor: | Artyom Y. Lebedev, and Anton S. Khartulyari, Alexander Z. Voskoboynikov |
|---|---|
| Rok vydání: | 2005 |
| Předmět: |
chemistry.chemical_classification
Indazole Intramolecular reaction Aryl Organic Chemistry Hydrazone chemistry.chemical_element General Medicine Chemical synthesis Combinatorial chemistry Catalysis chemistry.chemical_compound chemistry Intramolecular force Organic chemistry Chelation Amination Palladium |
| Zdroj: | The Journal of organic chemistry. 70(2) |
| ISSN: | 0022-3263 |
| Popis: | Palladium-catalyzed cyclization of arylhydrazones of 2-bromoaldehydes and 2-bromoacetophenones to give 1-aryl-1H-indazoles has been studied in detail. The cyclization of arylhydrazone of 2-bromobenzaldehydes can be performed with good to high yields using Pd(dba)2 and chelating phosphines, of which the most effective are rac-BINAP, DPEphos, and dppf, in the presence of Cs2CO3 or K3PO4 as a base. Electron-rich, bulky ligands commonly employed for intermolecular amination such as PtBu3 and o-PhC6H4PtBu2 were shown to be ineffective for cyclization and to lead instead to extensive oligomerization and tarring. The method developed is applicable for preparation of a wide scope of indazoles bearing electron-donating or electron-withdrawing substituents, among them, unprotected carboxyl, as well as various indazole heteroanalogues. The cyclization of arylhydrazones of less reactive halides such as 2-chlorobenzaldehyde, as well as 2-bromoacetophenone and bromotetralone, has been achieved. The purity of the starting hydrazone has been shown to be a critical parameter, as various impurities inhibit the cyclization. |
| Databáze: | OpenAIRE |
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