2- Aminopyrazole 1-oxide, preparation

Acylated 2-aminopyrazole 1-oxides 118 were prepared in excellent yields by heating (5-nitroacylhydrazones 117 to reflux with sodium methoxide in methanol (2006SL2731). The nitroacylhydrazones 117 were synthesized by treatment of 2-diaza-l,3-butadienes 115 with nitroalkanes 116 and catalytic amounts of sodium methoxide under solvent-free conditions at room temperature. The nitroalkane anion adds to the hydrazone 115 in a conjugated fashion producing diastereomeric mixtures of nitroac-ylhydrazone 117 in high yields (Scheme 36). 

The synthesis of 2,4,6-trisubstituted 2,6-dihydropyrazolo[3,4-d]-l,2,3-triazoles by the oxidation of 5-amino-4-azopyrazoles is well documented <86DP289,87IJC(B)616,88JHC1663). In a typical procedure, diazotized arylamines were coupled with 5-aminopyrazoles affording the required 5-amino-4-azo compounds, which were readily oxidized to the desired bicycle <86DP289, 87IJC(B)616>. Scheme 10 illustrates the preparation of a symmetric bispyrazolo[3,4-J]-1,2,3-triazole (25e) <86DP289>. Alter-... 

Most known monocyclic 1,2,3-triazines and 1,2,3-benzotriazines are stable at room temperature. No detailed study of the stability of monocyclic 1,2,3-triazines towards water, aqueous acids or bases has been published, but one can assume from the reaction conditions used in the preparation of monocyclic 1,2,3-triazines, by oxidation of (V-aminopyrazoles, that they are stable to water, aqueous acids or bases at room temperature, at least for a short time. Treatment of triaryl-1,2,3-triazines with aqueous hydrochloric acid at higher temperatures leads to hydrolysis of the ring and formation of 1,3-dicarbonyl compounds (Scheme 3) <60TL(13)19,76UP21800). 

Two 4-nitro-5-imino-2-pyrazolines are listed in Table XII. One of these was prepared by permanganate oxidation of the 4-oximino compound1010 and the other by direct nitration.1656 These compounds were believed to be aminopyrazoles rather than 5-imino-2-pyrazolines. 

Using various reagents, 1,2,3-triazines, including 1,2,3-triazine itself, can be prepared by the oxidation of 1-aminopyrazoles with NiOa or periodate. ... 

The first reported synthesis of 1,2,3-triazine involves the oxidation of 1-aminopyrazole with nickel peroxide other oxidants, such as lead tetraacetate, are ineffective, although they can be used to prepare substituted... 

Triazines have been prepared from five-membered rings as follows. The oxidation of 1-aminopyrazoles seems to be the most effective and widely applied method. Sodium periodate is the most efficient reagent for oxidation. In CHEC-II(1996) (p. 504), sodium perchlorate has been mentioned erroneously as the reagent instead of sodium periodate <1989H(29)1809> [additional reference <1992CEX321>]. LTA has been used to oxidize 1-or 2-aminoindazoles to 1,2,3-benzotriazines (CHEC(1984) and CHEC-II(1996)) [additional sources of... 

There were a couple of reports of cross-coupling reactions of pyrazoles published. Palladium-catalyzed cross-coupling between 3,4-, and 5-halopyr-azoles 32 and H-phosphonates, H-phosphinates, and secondary phosphine oxides to give pyrazoles 33 was accomplished in moderate-to-good yields (13OL5550). 1,3,5-Triarylaminopyrazoles 35 were prepared by Ullmann coupling firom l,3-diaryl-5-aminopyrazoles 34 and aryl halides in the presence ofcopper(I) iodide (13T570). 

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