3H-Pyrazol

Migrations of C- linked substituents around the ring, on to carbon or nitrogen atoms, are common amongst these compounds. This is the van Alphen-Huttel rearrangement and by it 3H-pyrazoles are converted into 1//-pyrazoles, and 2H-imidazoles are thermally iso-merized into IH-imidazoles. 

JA173) illustrates this possibility (Scheme 34). Thus 3,3,5-trimethyl-3//-pyrazole (371 R = H) on irradiation in pentane solution gives 1,3,3-trimethylcyclopropene (372 R = H) the intermediate diazoalkene (373) has been characterized. The tetramethyl derivative (371 R" = Me) when irradiated at -50 °C in methylene chloride leads to a species believed to be a l,2-dlazablcyclo[2.1.0]pent-2-ene (374). This isomerization is thermally reversible, the 3H- pyrazole being regenerated at room temperature. 

Pyrazole, N-vinyl-polymerization, 5, 269 3H-Pyrazole, 3,3,5-trimethyl-irradiation, 5, 251 Pyrazole carbaldehydes reactions, 5, 260 Pyrazole carbinols dehydration, 5, 261... 

Photolysis of the sulphinyl-3H-pyrazole 587 in ether or methylene chloride leads to the formation of a relatively stable carbene 588 that can be identified by physical methods. When the irradiation is performed in ethyl vinyl ether or in furan, the expected cyclopropanes are formed smoothly and stereospecifically683 (equation 374). 

It is known that certain coumarins are transformed into 5-(2-hydroxy-phenyl)-3H-pyrazol-3-ones by reaction with hydrazines [10]. Upon appUca-tion of this method, the expected pyrazolones 25 were synthesized starting from 3-nitrocoumarins [11] as known in (Scheme 6). 

Treatment of 4-methoxy-3-nitrocoumarin 23 with hydrazine hydrate and methylhydrazine in ethanol at room temperature for 3 h gave 1,2-dihydro-5-(2-hydroxyphenyl)-4-nitro-3H-pyrazol-3-one 24a and l,2-dihydro-5-(2-hydroxyphenyl)-2-methyl-4-nitro-3H-pyrazol-3-one 24b in 70 and 51% yields, respectively. 

Compound 24a was also obtained in 17% yield by heating of 4-hydroxy-3-nitrocoumarin 27 [12] with hydrazine hydrate in ethanol. A similar reaction of 27 with methylhydraine in boiling ethanol did not afford 24b because of the decomposition of the starting coumarin. However, when 27 was treated with methylhydrazine at room temperature for 24 h without solvent, the ring-opened methylhydrazine adduct 28 (36% yield) and 1,2-dihydro-5-(2-hydroxyphenyl)-l-methyl-4-nitro-3H-pyrazol-3-one 26 (ll%yield) were... 

However, 4-amino-l,2-dihydro-5-(2-hydroxyphenyl)-3H-pyrazol-3-one and 5-amino-6-6-(2-hydroxyphenyl)pyrimidin-4(3H)-one appear to be interesting structures for developing new analgesic agents. 

We now report the synthesis of new antibacterial 3H-pyrazoles by regioselective 1,3-dipolar cycloaddition of the versatile 2-diazopropane to nonprotected disubstituted propargyl alcohols and that the unsubstituted propar-gyl alcohol allows the double addition of 2-diazopropane and gives a 3H-pyrazole with formal insertion of the dimethylcarbene into a carbon-carbon bond. We also show that the photolysis of the 3H-pyrazoles leads to new alcohols containing the cyclopropenyl unit. 

The antibacterial activity of the obtained 3H-pyrazoles 63a,b and 64 has been studied. They have been tested opposite a pathogenic bacterial stump and have shown antibacterial activity against the original Staphyloccocusaureus. The 3H-pyrazole 63b offers the strongest antibacterial activity [56]. 

Photochemical Transformation of the Obtained 3H-Pyrazoles into Cyclopropene Derivatives... 

The photochemical study of 3H-pyrazoles was carried out in the search for a route to cyclopropenyl tertiary alcohols. Irradiation of 63a in dry dichloromethane at 300 nm and at room temperature for 0.5 h led to the exclusive formation of the gem-dimethylcyclopropene 65 (Scheme 17). The formation of cyclopropene 65 arises from the loss of N2 and cycUzation of the vinylcarbene intermediate (III). 

The analogous photochemical reaction (300 nm) of 3H-pyrazole 64 in dichloromethane at room temperature led to cyclopropene derivative 66, possessing a a-hydroxy group, isolated in 70% yield (Scheme 18). 

This study demonstrates that the addition of the 2-diazopropane with the triple bond of propargyl alcohols is regioselective, and affords new antibacterial 3H-pyrazoles. The photochemical reaction of these 3H-pyrazoles selectively leads to a- and 6-hydroxy cyclopropenes. The overall transformation constitutes a simple straightforward route to substituted cyclopropenyl alcohols without initial protection of the propargyl alcohol hydroxyl group. 

Bromophenylazo)-2-propyl hydroperoxide, 3156 l,2-Dihydroperoxy-l,2-bis(benzeneazo)cyclohexane, 3762 (Y-Phcnylazobcnzyl hydroperoxide, 3609 a-Phenylazo-4-bromobenzyl hydroperoxide, 3607 1-Phenylazocyclohexyl hydroperoxide, 3539 a-Phenylazo-4-fluorobenzyl hydroperoxide, 3608 3,3,5-Triphenyl-4,4-dimethyl-5-hydroperoxy-4,5-dihydro(3H)pyrazole, 3841... 

Antipyrine (l,2-dihydro-l,5-dimethyl-2-phenyl-3H-pyrazole-3-one) is anM-me-thylated analgesic drug which is primarily metabolized in the liver by microsomal cytochrome P450 enzymes [3, 61-68] (Fig. 3). The three main oxidative metabolites of antipyrine are 4-hydroxyantipyrine, 3-hydroxymethylantipyrine, and norantipyrine. 

Bei Kupplungsreaktionen von Aryldiazonium-Salzen mit 2-Alkoxy-l,6-methano-[10]an-nulenen entstehen meistens unter Ether-Spaltung uberbruckte 5-Arylhydrazono-2-oxo-1,6-methano-10,3,6,8-cyclodecatetraene. 3-Diazo-3H-pyrazole und -indazole liefern je-doch die Azo-Verbindungen unter milden Kupplungsbedingungen in guten Ausbeuten (bereits bei pH = 5 entstehen ebenfalls die Chinon-hydrazone) ... 

Die Umsetzung von 2-Acylamino-2-alkensaure-estem mit Diazo-alkanen liefert als Zwi-schenprodukt 4,5-Dihydro-3H-pyrazole, die beim Erhitzen unter Verlust von Stickstoff und nach der Hydrolyse N-geschiitzte 1-Acylamino-l-carboxy-cyclopropane erge-ben2 4 ... 

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