3.4- dimethyl-l-pyrazoline

Lack of stereospecificity, extensive formation of olefinic products, and extensive tar formation limit the thermal decomposition of pyrazolines as a route to cyclopropanes.182 263 Light-induced decomposition of stereoisomeric pyrazolines establishes a method for the formation of cyclopropanes stereospecifically.222 Photolysis of 3-carbomethoxy-cis-3,4-dimethyl-l-pyrazoline (CCLI) produced cis-l,2-dimethylcycIopropane-l-carboxylate (CCLII) and without olefinic formation. Furthermore, irradiation of 3-carbomethoxy-trans-3,4-dimethyl-l-pyrazoline (CCLIII) gave [Pg.123]

Pyrazolines, in general, undergo a photochemically induced ring contraction in solution to form a cyclopropane derivative and nitrogen. This process, unlike some equivalent thermal decompositions, is stereospecific, and methyI-as-3,4-dimethyl-l-pyrazoline-3-carboxyl-ate (88) is converted in high yield into methyl-as-1,2-dimethylcyclo-propane carboxylate (89).69 This route is of considerable preparative... 

Pyrazoline Derivatives. Triplet biradicals (308) are postulated as intermediates in the photolysis of cis- and /ra/i -3,4-dimethyl-l-pyrazoline. The characteristic trans .cis ratio of the cyclopropane products (309) expected... 

Garbomethoxy-trans-3,4-dimethyl-l-pyrazoline irradiated 43 hrs. with a GE sunlamp l-carbomethoxy-frans-l,2-dimethylcyclopropane. Y 72%. Also with the c/s-isomer s. T. V. Van Auken and K. L. Rinehart, Jr., Am. Soc. 8A, 3736 (1962). 

Verkade and Dhont1531 have treated 3,4-dimethyl-2-pyrazolin-5-one and 4-methyl-3-phenyl-2-pyrazolin-5-one with phenyldiazonium chloride, forming respectively 3,4-dimethyl-2-phenylazo-3-pyrazolin-5-one, m.p. 273°, and 4-methyl-3-phenyl-2-phenylazo-3-pyrazolin-5-one, m.p. 212°. 2,3-Dimethyl-l-phenyl-3-pyrazolin-5-one reacts with thio-oyanogen to give its thiocyanate salt and 2,3-dimethyl-l-phenyl-4-thiocyanato-3-pyrazolin-5-one, m.p. 125°.742... 

From Pyrazolines. —The decomposition of A -pyrazolines to cyclopropanes may be photochemically or thermally induced and the mechanisms of both processes are still under active investigation. Both trans- and cis-3,4-dimethyl-A -pyrazolines (90a) and (90b) give trans- and ds-l,2-dimethylcyclopropanes... 

Pyrazoline, 3,4-dimethoxycarbonyl-l-phenyl- H NMR, 5, 189 2-Pyrazoline, 5,5-dimethyl-tautomerism, 5, 216 2-Pyrazoline, 1,3-diphenyl- H NMR, 5, 189... 

The desilylacetylated qrcloadducts, produced from the reactions of trimethylsilyl-diazomethane with 3-crotonoyl-2-oxazolidinone or 3-crotonoyl-4,4-dimethyl-2-oxa-zolidinone, were transformed to methyl traws-l-acetyl-4-methyl-l-pyrazoline-5-car-boxylate through the reactions with dimethoxymagnesium at -20 °C. When the optical rotations and chiral HPLC data were compared between these two esters, it was found that these two products had opposite absolute stereochemistry (Scheme 7.39). The absolute configuration was identified on the basis of the X-ray-determined structure of the major diastereomer of cycloadduct derived from the reaction of trimethylsilyldiazomethane to (S)-3-crotonoyl-4-methyl-2-oxazolidi-none. 

The data in Tables XVI and XVIII reveal a general tendency for the 1,3,4-thiadiazoline tautomer 86B to predominate in the series of 1,3-diketone and 3-oxoaldehyde thiobenzoylhydrazones. The increased stability of the tautomer 86B is attributable to the greater nucleophilicity of the sulfur atom as compared with that of nitrogen, and to the lower strain of the ring containing the sulfur atom. As can be foreseen (see 84ZOR169), pentane-2,4-dione thiophenylacetylhydrazone exists as stable 5-hydroxy-2,4-dimethyl-l-thiophenylacetyl-2-pyrazoline (84ZOR180). 

Mercaptomethyl-2,4-dimethyl-l-phenyl-3-pyrazolin-5-one in dimethy Iformamide as aprotic solvent added to a soln. of Na in abs. ethanol, excess of which is then distilled off under reduced pressure, 2-nitrochlorobenzene in dimethylform-amide added, and heated 1 hr. at 90-100° on a water bath 2-(2,4-dimethyl-l-phenyl-3-pyrazolin-5-on-3-yl)methylthionitrobenzene. Y 80%. F. e. s. I. Ito and T. Ueda, Chem. Pharm. Bull. 17, 1309 (1969). 

Scheme 19 contains all the reactions observed in different examples, none being so complex (B-76MI40402). Most studies deal with the methylation of 3-methyl-1-phenyl-pyrazolone, since in this case one of the products obtained is antipyrine (2,3-dimethyl-l-phenyl-3-pyrazolin-5-one), one of the classical antipyretic agents (Section 4.04.4.1.1). 

Dippii solution I Dissolve 1 g 4-aminoantipyrine (4-aminophenazone 4-ami-no-2,3-dimethyl-l-phenyl-3-pyrazolin-5-one) in 100 ml 80% ethanol. 

The reaction of aroylhydrazines with DMAD gives rise to the hydrazones of oxaloacetic ester, which undergo thermal transformation to the corresponding diaroylhydrazines. b. Hydrazones. Ethyl l,3,5-triphenylpyrazole-4-carboxylate has been reported to be formed in the reaction of benzaldehyde phenylhydrazone with ethyl phenylpropiolate. In a detailed investigation, George and co-workers have shown that aldehyde phenylhydrazones react with DMAD, yielding a mixture of pyrazoles and pyrazolines. Thus, in the reaction of benzaldehyde phenylhydrazone with DMAD, products such as dimethyl l,3-diphenylpyrazoline-4,5-dicarboxylate (129), dimethyl... 

The electrochemical oxidation of 4-dimethylaminoantipyrine (4-dimethyl-amino-2,3-dimethyl-l-phenyl-A3-pyrazolin-5-one) has been investigated in CH3CN-NaC104 at a glassy carbon electrode.421 The first step is a quasi-reversible electron transfer from the lone-pair electrons on the 4-dimethyl-amino nitrogen to form the radical-cation. The second-order disappearance of the radical-cation is presumably due to a disproportionation reaction. The oxidation at the potential of the plateau of the first wave gave the protonated 4-dimethylaminoantipyrine in 60% yield, but other products were not identified. 

Antipyrine or 2,5-Dimethyl-l-phenyl-4-pyrazoline-3-one, listed in Beil as 1-Phenyl-2.5-dimethyl-pyrazolon-(3),(HjC)C-N(C6H5)-N(CHj)... 

The results of Katritzky and co-workers [74JCS(P2)382], who carried out an extended study of such systems, are shown in Fig. 10. These indicate that all six compounds studied reacted as the conjugate acid at high acidity. Three compounds also reacted as the conjugate acid at low acidity [3-methyl-4-nitro-l-phenylpyrazolin-5-one, 3-methyl-5-methoxy-4-nitro-l-phenyl pyrazole, and 3-methyl-5-methoxy-l-(4-nitrophenyl) pyr-azole]. The other three compounds [2,3-dimethyl-4-nitro-l-phenylpyraz-olin-5-one, 3-methyl-1-(4-nitrophenyl) pyrazolin-5-one, and 2,3-dimethyl-1-(4-nitrophenyl) pyrazolin-5-one] reacted as free bases at low acidity. 

In the case of the reaction of perfluoro-2-methylpent-2-ene with 1,1-dimeth-ylhydrazine in the presence of triethylamine as the dehydrofluorinating agent and Et20 as a solvent at —50 to 0°C, the product is 5,5-difluoro-l,l-dimethyl-3-pentafhioroethyl-4-trifluoromethyl-1 -pyrazolin-2-yl 64 (87RP14 56418, 90IZY2583). 

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