Reactivity of 1-(2-bromobenzyl)-4-halopyrazoles in intermolecular and intramolecular Pd-catalysed direct arylations

TETRAHEDRON

卷:72

Article

Brahim, Mariem^1,2  Ben Ammar, Hamed²  Soule, Jean-Francois¹  Doucet, Henri¹ 

[1] Univ Rennes, Inst Sci Chim Rennes, Organometall Mat & Catalyse, CNRS,UMR 6226, Campus Beaulieu, F-35042 Rennes, France

[2] Univ Monastir, Fac Sci Monastir, Lab Synth Organ Asymetr & Catalyse Homogene, UR 11ES56, Ave Environm, Monastir 5000, Tunisia

关键词: Palladium;    Catalysis;    C-H bond activation;    Pyrazoles;    Direct arylation;    Aryl halides;   

DOI  :  10.1016/j.tet.2016.05.079

来源: Elsevier

【 摘 要 】

The reactivity of 1-(2-bromobenzyl)-4-halopyrazoles in inter- and intra-molecular Pd-catalysed direct arylation was investigated. Conditions allowing the intermolecular C5-arylations of both 1-(2-bromobenzyl)-4-chloropyrazoles and 1-(2-bromobenzyl)-4-bromopyrazoles, without cleavage of the pyrazolyl and benzyl C-halo bonds, are reported. Using KOAc as the base, DMA as the solvent and 2 mol % of an air stable palladium catalyst, the target C5-arylated pyrazoles were obtained in moderate to good yields with a wide variety of aryl bromides. The synthesis of 3-halopyrazolo[5,1-a]isoihdoles via intra-molecular Pd-catalysed direct arylation, without cleavage of the pyrazolyl C-halo bonds is also described. Moreover, sequential Pd-catalysed C5-arylations followed by intramolecular direct arylation allowed the access to dibenzo[c,e]pyrazolo[1,5-a]azepine derivatives. The reactivity of the 2-bromobenzyl moiety of C5-arylated 1-(2-bromobenzyl)-4-halopyrazoles in intermolecular direct arylation or in Suzuki coupling is also described. (C) 2016 Elsevier Ltd. All rights reserved.

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