Palladium-catalysed direct diarylations of pyrazoles with aryl bromides: a one step access to 4,5-diarylpyrazoles

Conditions for palladium-catalyzed direct arylations of 4-bromo and 4-iodo N-substituted pyrazoles without C–Br or C–I bond cleavage

“…13 The diarylation of pyra-zole derivatives at C4 and C5 positions has also been reported using an excess of arylbromides. 14 Similar approaches, namely, regioselective Pd-catalyzed direct arylations of haloheteroarenes have also been reported. 15 Here, we investigated the direct arylation of 4-bromo-1-( protected)pyrazole derivatives using a simple catalytic system based on palladium and also extended this reaction to more challenging 4-iodo-1-( protected)pyrazole derivatives (Fig.…”

“…2a). In 2013, Bellina obtained a higher C5 : C4 ratio (i.e., 86 : 14) without formation of a diarylated product, using Bu 4 NOAc as the base (Fig. 5 Again, the reaction was not regioselective and a mixture of C5,C4 arylated and diarylated products was obtained in a 78 : 16 : 6 ratio.…”

Intermolecular versus Intramolecular Palladium‐Catalyzed Direct Arylations between 1‐(2‐Bromobenzyl)imidazoles and Aryl Bromides

“…This result strongly suggests that an electron‐deficient arene is required to get a cyclization reaction. On the other hand, we prepared 4,4′‐(1‐(2‐bromobenzyl)imidazole‐2,5‐diyl)dibenzonitrile ( 38 ) from 1‐(2‐bromobenzyl)imidazole using our previous “one‐pot” procedure 16c. Product 38 was obtained in low yield and could not be isolated in pure form, therefore, we decided to perform the cyclization reaction on the crude mixture.…”

Iron(III) phthalocyanine chloride-catalyzed oxidation–aromatization of α,β-unsaturated ketones with hydrazine hydrate: Synthesis of 3,5-disubstituted 1H-pyrazoles

“…Because of the importance of pyrazole derivatives, significant efforts have been devoted to developing new methods for their synthesis. Pyrazoles are generally synthesized by (1) reacting hydrazines with 1,3-dicarbonyl compounds/unsaturated hydrocarbons [28][29][30][31][32][33][34], (2) 1,3-dipolar cycloaddition of diazoalkanes with alkenes or alkynes [35][36][37][38][39][40][41][42], (3) reacting α,β-unsaturated carbonyl with hydrazines [43][44][45][46], and various other strategies [47][48][49][50][51][52][53]. However, these methods often re-quire harsh reaction conditions (stoichiometric strong base, high reaction temperature), precious-metal catalysts, and stoichiometric and environmentally unfriendly oxidants.…”