Pyrazoles arylhydrazones

Surprisingly, arylhydrazones 88a-d, upon treatment with 1-benzenesulfonyl-hydrazide 89 in refluxing ethanol, afforded very good yields of pyrazol-3-ones 90a-d (85JIC54) (Scheme 25). 5-Aminopyrazol-3-(Mies have also been synthesized from /3-cyanoesters (Section II,A,2) and from /3-iminoesters (Section II,A,3). 

Oxidation of arylhydrazones 143 with HTIB in the presence of diisopro-pylethylamine produces pyrazoles 145 in one pot. The intermediate a-tosyloxy compounds 144, which are generated in situ by the oxidation of 143, undergo intramolecular participation of amino group in displacement of the tosyloxy group, thereby yielding cyclized products 145 (91SC1583). 

Arylhydrazones of /3-aryl-a,/3-unsaturated ketones are converted into pyrazoles by 3 mol equivalents of T CIO4 (Scheme 2). The ring closure occurs via radical cation 45 and is not simply oxidation of a preclosed dihydropyrazole, as evidenced by dimerization (- 46) of such a possible intermediate upon treatment with the radical cation (Scheme 3) (88JOC1973). 

A series of pyrazoles was obtained by azo-coupling of acetoacetic ester derivatives and cyclization of the arylhydrazones formed.219-229 Probably a similar type of reaction occurs with p-nitrophenyldiazo-... 

The functionality needed for cyclization may be incorporated in the ketone, as exemplified in one entry of Table 7.3. Intramolecular participation was also provided by arylhydrazones derived from ethyl acetoacetate, with aryls having electron-withdrawing substituents when heated with HTI and a tertiary amine, they were transformed to ethyl l-aryl-4-hydroxy-pyrazole-3-carboxylates [37] ... 

Hydrazones are useful intermediates in the preparation of pyrazoles. 3-Oxo-3-(pyrrol-2-yl)-propanenitrile 9 was coupled with aromatic diazonium salts to yield the corresponding 2-arylhydrazones 10, which then reacted with chloroacetonitrile and ethyl chloroacetate to yield 4-aminopyrazole derivatives 11 <07SC3579>. The cyclization of hydrazone dianions of 12 with diethyl oxalate 13 afforded pyrazole-5-carboxylates 14 <07TL3591>. 

Arylhydrazone von 3-(l-Adamantyl)-3-chlor-acrolein und 3-(l-Adamantyl)-3-chlor-2-methyl-acrolein geben beim Erhitzen in einem Phosphorsaure/Essigsaure-Gemisch661 oder in Phos-phorsaure6625-( l-Adamantyl)-l-( 2,4-dinitro-phenyl)-(41 % Schmp. 163,5 165,5°), 5-( 1-Ada-mantyl)-l-(2,4-dinitro-phenyl)-4-methyl- (54% Schmp. 199,5-200,5°)661 bzw. 5-( 1-Adaman-tyl)-1-phenyl-lH-pyrazol (48% Schmp. 135-136°)662 ... 

Fluorine-containing 2-arylhydrazone-l,2,3-diketo esters, 2-arylhydrazones of 1,2,3-triketones and 3-arylhydrazone-l,2,3,4-triketo esters may serve as key precursors to a variety of novel heterocycles and react with binucleophiles (85UK1997, 81UK325, 94ZOR1225). Thus, the 1,2,3-triketones arylhydrazones react with hydrazine hydrate, phenylhydrazine, thiosemicarbazide, and hydroxylamine hydrochloride to form the substituted pyrazoles and isoxazoline (98JFC(92)101, 98IZV673) (Scheme 53). 

Although the action of acetic anhydride on sugar arylhydrazones gave only the respective per-acetyl derivatives, the hydrazones 20, derived from ascorbic acids, gave the pyrazole derivative 21 which can also be prepared xmder microwave irradiation (El Ashry et al., impubhshed results) [49,50]. 

A-Arylhydrazones are useful agricultural materials. Moreover, they can be cleaved to form A-arylhydrazines for pyrazole synthesis, and the hydrazine portion can be transferred to ketones to serve as substrates for the Fischer indole synthesis.t The reactions of benzophenone hydrazone with aryl halides have been reported, and to date these reactions are best conducted with chelating phosphine ligands such as DPPF and BINAP, as shown in Eq. 22. These catalyst systans have been the only ones reported for hydra-zone arylation. The chemistry of hydrazonato complexes is similar to that of aniUdes and diarylamides.f Thus, the reactions of aryl chlorides with hydrazones should be accessible in the future using alkylphosphine ligands. 

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