Pyrazoles Raney nickel

When the pyrazole ring forms part of a condensed structure and has a 3-hydroxyl group (or tautomer), the N—N link may be hydrogeno-lyzed comparatively smoothly by boiling an alcoholic solution of the compounds with Raney nickel.742,743... 

They can be replaced with hydrogen atoms by catalytic (Pd, Ni, etc.) or chemical reduction (HI or Zn/H2S04). For example, halopyrazoles with HI and red phosphorus at 150C give pyrazoles, and 5-bromo-l,2,4-thiadiazole is reduced by Raney nickel to the parent heterocycle. 2-Bromothiazole can be reduced electrochemically. 

Isoxazoles bearing alkyl or carbamoyl groups were transformed into the corresponding pyrazoles in high yields by treatment with hydrazine in methanol in the presence of a hydrogenation catalyst such as Raney nickel, at room temperature <07T12195>. 

Zur Einfiihrung des Isopropyl-Restes in die 4-Position muB das Knoevenagel-Kondensations-produkt nicht isoliert werden so fiihrt z. B. die Hydrierung von 5-Hydroxy-3-methyl-l-phenyl-lH-pyrazol in Aceton mit Raney-Nickel direkt zu 5-Hydroxy-4-isopropyl-3-mcthyl-l-phenyl-IH-pyrazol (78% Schmp. 114-1150)416. 

Amino-l-tert.-bntyl-lH-pyrazol164 Eine Losung von 42,3 g (0,25 mol) l-tert.-Butyl-4-nitro-lH-pyrazol in 250 ml Ethanol wird in Gegenwart von 5 g Raney-Nickel bei 50° unter 5,5 MPa Wasserstoff-Druck hydricrt. Nach Abfiltrieren des Katalysators wird i. Vak. eingeengt und dcr Riickstand destilliert Ausbeute 27,8 g (80%) Sdp. 65°/0,l Torr (13 kPa)] (erstarrendes gelbcs Ol) Schmp. 60. ... 

Pyrazoles. Isoxazoles are readily converted into pyrazoles on treatment with hydrazine at room temperature in the presence of Raney nickel. ... 

Khaikin et al. (65ZOR133) (Scheme 200) reduced thirteen ( /Z)-pyrazol-3-one-4-oximes 685a,b by catalytic hydrogenation in ethanol at 40-50 °C using Raney nickel catalyst, and obtain fairly good yields of the corresponding 4-aminopyrazol-3-one hydrochlorides 686a,b. 

Pyrazolo[3,4-b]pyrazines are useful intermediates for the preparation of 2-aminopyrazine-3-carboxamides such as 49, much used in pteridine syntheses. For example, reductive cleavage of the 1-substituted 3-hydroxy compound 48 with Raney nickel results in smooth breakdown of the pyrazole ring to give the product 49. 

The pyrazole is then chlorinated in the 4 position and saponified to give the pyrazolecarboxylic acid. The acid chloride of the pyrazolecarboxylic acid is formed and coupled with 4-tert-butylbenzylamine or 4- p-tolyloxy)benzylamine to give tebufenpyrad and tolfenpyrad, respectively. The side chain compound 4-tert-butylbenzylamine is prepared by the reductive amination of 4-tert-butylbenzal-dehyde with aqueous ammonia. The compound 4-(p-tolyloxy)benzylamine is prepared by coupling 4-fluorobenzonitrile with sodium p-cresol followed by reduction with Raney nickel in aqueous ammonia [47, 48]. 

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