Pyrazolines, reaction with

PyraZolines. l,3-Diphenyl-2-pyia2olines (7) (Table 2) aie obtainable from appiopiiately substituted phenyUiydiazines by the Knoii reaction with either P-chloro- or P-dimethylaminopropiophenones (30,31). They are employed for brightening synthetic fibers such as polyamides, cellulose acetates, and polyacrylonitriles. 

The methylhydrazone of acetophenone (112) underwent ready reaction with n-butyl-lithium giving the dianion (113) reaction with acid derivatives such acid chlorides or esters resulted in pyrazole (114) formation whereas with aldehydes, pyrazolines were obtained (76SC5). With dichloromethyleneiminium salts (115), 5-dimethylaminopyrazoles... 

Pyrazolones show a great variety of reactions with carbonyl compounds (B-76MI40402). For instance, antipyrine is 4-hydroxymethylated by formaldehyde and it also undergoes the Mannich reaction. Tautomerizable 2-pyrazolin-5-ones react with aldehydes to yield compound (324) and with acetone to form 4-isopropylidene derivatives or dimers (Scheme 8 Section 4.02.1.4.10). 

Hi) Electrochemical reactions and reactions with free electrons Electrochemical oxidation of 3-methyl-l-phenylpyrazole gave the 3-carboxylic acid whereas electrochemical reduction (Section 4.04.2.1.6(i)) of l,5-diphenyl-3-styrylpyrazole produced the A -pyrazoline (B-76MI40402) with concomitant reduction of the exocyclic double bond (343). 

Analogous to the oxidation of hydrazones to azo compounds, A-unsubstituted pyrazolidines are oxidized to A -pyrazolines. For example, the blcyclic pyrazolidine (415) when treated with silver oxide yields the pyrazoline (416) (65JA3023). Pyrazolidine (417) is transformed into the perchlorate of the pyrazolium salt (411) by reaction with mercury(II) acetate in ethanol followed by addition of sodium perchlorate (69JOU1480). 

Azomethines add with great ease and stereospecificity to carbon-carbon double bonds affording pyrazolidines. They also add to carbon-carbon triple bonds with the formation of pyrazolines. Benzimidazolium iV-imines, e.g. (622), are a special case of azomethines. Its reaction with DMAD yields l-(2-methylaminophenyl)pyrazole (624), which is formed by cleavage of the initial adduct (623) (75JHC225). 

Johnson and co-workers also investigated the general acid-catalyzed diazomethane reaction with benzalacetone (20). When treated with 3 mole-equivalents of diazomethane, the latter is converted to the A -pyrazoline... 

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 preparation of cyclopropane derivatives has been greatly facilitated by the development of carbene-type intermediates (see Chapter 13) and their ready reaction with olefins. The preparation of phenylcyclopropane from styrene and the methylene iodide-zinc reagent proceeds in only modest yield, however, and the classical preparation of cyclopropane derivatives by the decomposition of pyrazolines (first employed by Buchner in 1890) is therefore presented in the procedure as a convenient alternative. 

There is much evidence that the mechanism" of the 1-pyrazoline reactions generally involves diradicals, though the mode of formation and detailed structure (e.g singlet vs. triplet) of these radicals may vary with the substrate and reaction conditions. The reactions of the 3 f-pyrazoles have been postulated to proceed through a diazo compound that loses N2 to give a vinylic carbene." ... 

Ketene dithioacetal 130 reacts with 3-amino-2-pyrazolin-5-one 129 to give the highly functionalized pyrazolopyridine 131, which is converted into the bispyrazolopyridine 132 by reaction with hydrazine hydrate (Scheme 9) <1997JCM256>. 

Palladium-catalyzed cyclization reactions with aryl halides have been used to synthesize pyrazole derivatives. V-Aryl-lV-(c>-bromobenzyl)hydrazines 26 participated in a palladium-catalyzed intramolecular amination reaction to give 2-aryl-2W-indazoles 27 . Palladium-catalyzed cascade intermolecular queuing-cyclocondensation reaction of o-iodophenol (28) with dimethylallene and aryl hydrazines provided pyrazolyl chromanones 29 <00TL7129>. A novel one-pot synthesis of 3,5-disubstituted-2-pyrazolines 32 has been achieved with an unexpected coupling-isomerization sequence of haloarene 30, propargyl alcohol 31, and methylhydrazine <00ACIE1253>. 

Diphenylcyclopropane has been prepared in 24% yield by the Simmons-Smith reaction,2 in 78% yield by treatment of 3,3-diphenylpropyltrimethylammonium iodide with sodium or potassium amide,3 in 61% yield by reaction of 1,1-diphenyl-ethylene with dimethylsulfonium methylide,4 and in unspecified yields from 1,1-diphenylethylene by reaction with diazomethane followed by pyrolysis of the resulting pyrazoline or by reaction with ethyl diazoacetate followed by distillation of the corresponding acid over calcium oxide.5... 

Arenes, polyalkyl, oxidation with per-oxytrifluoroacetic acid and boron trifluoride, 48, 89, 90 Arenesulfonyl chlorides, reaction with 3-amino-3-pyrazoline, 48, 11 Aromatic aldehydes. Mesitalde-HYDE, 47, 1... 

Imidazole, purification of, 48, 45 reaction with phosgene, 48, 44 Imldazole, 1,1 -carbonyldi-, 48, 44 Imidazolium chloride, 48, 46 3-Imino-l-( -tolylsulfonyl)pyrazolidine, from 3-amino-3-pyrazoline sulfate and / -toluenesulfonyl chloride, 48, 9... 

Reaction of isatin or thioisatin 263 with (R)-(—)-thiaproline afforded thiazolo-oxazolidinones 264 as precursor of azomethine ylides, obtained by decarboxylation, for 1,3-dipolar cycloadditions (Equation 116) <2002SC435, 2004PS2549>. Condensation of 5-(alkylamino)methyl-2-pyrazolines 265 with ketones or aldehydes led to tetrahy-dro-imidazo[l,5-7]pyrazoles 266 (Equation 117) <1998JCCS375>. 

The transition metal-catalyzed reaction of diazoalkanes with acceptor-substituted alkenes is far more intricate than reaction with simple alkenes. With acceptor-substituted alkenes the diazoalkane can undergo (transition metal-catalyzed) 1,3-dipolar cycloaddition to the olefin [651-654]. The resulting 3//-pyrazolines can either be stable or can isomerize to l//-pyrazolines. 3//-Pyrazolines can also eliminate nitrogen and collapse to cyclopropanes, even at low temperatures. Despite these potential side-reactions, several examples of catalyzed cyclopropanations of acceptor-substituted alkenes with diazoalkanes have been reported [648,655]. Substituted 2-cyclohexenones or cinnamates [642,656] have been cyclopropanated in excellent yields by treatment with diazomethane/palladium(II) acetate. Maleates, fumarates, or acrylates [642,657], on the other hand, cannot, however, be cyclopropanated under these conditions. 

Diazomethane is capable of addition reactions with double bonds. Pyrazoline rings are formed. Studebaker et al. (38) saw in this reaction an indication of quinone groups ... 

Enantiomerically pure nitrile imines (211) have also been generated by the lead tetraacetate oxidation of aldehydo sugar p-nitrophenyl hydrazones. Reaction with methyl acrylate gave the pyrazolines as a 1 1 mixture of the (55) and (5R) epimers, which were resolvable in some cases (116). 

Similar to their reaction with phosphaalkenes, l-diazo-2-(oxoalkyl)silanes 29 react with various heterophospholes by [3 + 2] cycloaddition of the diazocumulene system 30 (which is in equilibrium with 29) across the P=C bond. With 2-acyl-1,2,3-diazaphospholes 119 (R = Ac, Bz no reaction with R = Me, Ph up to 60 °C), the expected cycloaddition products 120 (Scheme 8.27) could be isolated (186). Elimination of N2 from these bicyclic A -pyrazolines occurred upon heating at 100 °C and furnished the tricyclic systems 122 when SiRs was a trialkylsilyl group. Apparently, the thermolysis of 120 generates the 5-aIkenylidene-l,2,5-diazaphosphole 121 (by N2 extrusion) as well as diazaphosphole 119 (by a [3 + 2] cycloreversion process), which recombine in an intermolecular cycloaddition to furnish 122. When SiRa = SiPhaf-Bu, a formal intramolecular [3 + 2] cycloaddition of the C=P=C unit with an aromatic C=C bond occurs and the polycyclic compound 123 is obtained (187). 

A number of 2-acyI-l-chIoroethenes add to DPD in ether, losing HC1 spontaneously from the intermediate pyrazolines, and giving l/f-pyrazoles from rearrangement of the transient 3H isomers.50,60 The acid chloride 36 gives a small amount of a 3//-pyrazoIe 37 from reaction with two moles of methyl diazoacetate (Scheme 12).88... 

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