Pyrazoline derivative

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 

The acetolysis of the 1-pyrazoline (310) probably proceeds via a diazonium ion (311). The evidence cited for this conclusion includes the nature of the 

2-Alkynoic esters (315) are available in one step by treatment of the readily accessible pyrazolones (316) with two equivalents of thallium(in) nitrate in 

The Curtius reaction of l-phenyl-3-azidocarbonyl-2-pyrazolin-5-one (320) in glacial acetic acid does not lead to the expected product (321), giving instead 2-acetyl-3-amino-l-phenyl-3-pyrazolin-5-one (322). A six-membered transition state involving the intermediate mixed anhydride (323) is proposed. 

Copper(ii)-catalysed aerial oxidation of pyrazol-5-ones (324) gives the meso and racemic forms of 4-(5 -oxopyrazolinyI)pyrazol-5-ones (325).  

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The salts (71) and (72) are both A -pyrazoline derivatives. However, the first one is obtained by quaternization of a A -pyrazoline and the second one by protonation of a A -pyrazoline (Section 4.04.2.2.2(v)). Several A -pyrazolinium salts (72) and their NMR spectra are described in (69BSF3292,71T123) and for A -pyrazolinium salts (73) see (69BSF3316). 

The same group has published two articles on indazoles [indazole (36), 1-methyl- (106) and 2-methyl-indazole (107)]. The He-I and He-II spectra have been obtained and satisfactorily interpreted by means of ab initio LCGO calculations (78JST(43)33, 78JST(43)203). The PE spectra support the conclusion (Section 4.04.1.5.1) that the 1//-tautomer is by far the more stable. X-Ray photoelectron spectra of some pyrazole and pyrazoline derivatives have been reported (83MI40400). 

Spiro-pyrazoline derivatives (18) are obtained smoothly from 16-methy-lene-17-ketones (17). ° The sole products formed from (18) by pyrolysis or cleavage in the presence of boron trifluoride etherate, are the 16-spiro-cyclopropyl steroids (19). ... 

For a convenient photochemical preparation of steroidal a-cyclopropyl ketones from the A -pyrazoline derivatives of the corresponding a, -unsaturated ketones, cf. ref. 50. 

It was found, during a study of synthetic routes leading to quinine analogues, that oxidation of a specific bicydic pyrazoline derivative with mercuric acetate gives an enamine-like pyrazole (87b). 

Diazoalkanes add readily to the double bond of esters of vinylphosphonic acid, giving the pyrazoline derivatives (100), which can lose nitrogen to give esters of cyclopropylphosphonic acids. In a similar reaction, acyl-phosphonic acid esters (101) were converted to epoxy-derivatives (102). A -Phenylsydnone adds to diethyl prop-l-ynephosphonate, giving the pyra-zole (103). The addition of cyclopentadiene to dimethyl vinyl phosphate leads to an exojendo quotient of 1.2, but with hexachlorocyclopentadiene only e/ii/o-isomer is formed. ... 

Table 6.38 PYRAZOLINE DERIVATIVES AND RIMONABANT (382) - IN VIVO DATA...

Protected pyrazoline derivatives 429 can be transformed by conventional ozonolysis methodology to the corresponding aldehydes 430, then the Cbz protecting group is removed and the intramolecular reductive amination using... 

The (5 5 5) fused heterocycles have also been synthesized from enedione 88 by utilizing its susceptibility to the nucleophilic attack. The enedione 88 was accordingly treated with excess of ethereal diazomethane in methanol at 4°C to afford the 7 -methyl derivative 31 presumably via 374 which was not isolated. 2-Pyrazoline derivative 31 was isolated in 46% yield under the same reaction conditions at room temperature (Scheme 80) <2002OL4387>. 

Scheme 7 shows formation of a new fused ring described by Mohan and Kataria <1998IJB819>. These authors reported that treatment of the benzylidene compound 19 with hydrazine hydrate in acetic acid in the presence of sodium acetate gave the tricyclic fused pyrazoline derivative 20 in acceptable yield (61%). The two hydrogen atoms at the site of the ring closure were found to be as. 

The pyrazoline derivative 260 was also the precursor for the synthesis (252) of the naturally occurring umbelactone. Reaction of butenolide 159c with diazomethane gave the pyrazoline 260, which was subjected to pyrolysis to give (—)-(5 )-umbelactone (261). As the natural umbelactone was described as being dextrorotatory, the synthesis of (+)-(R)-umbelactone from 159c was also performed. 

The flavazoles, an interesting type of pyrazoline derivative obtained by interacting sugar quinoxalines with phenylhydrazine, will be discussed in the next Section (see p. 398). 

Pyrazoline derivatives have attracted considerable attention, and their electrochemical oxidation, studied in aqueous277,278 and nonaqueous media,279-290 led to different products, depending on the structure of the starting pyrazoline and the media. The intermediate bis(pyrazolinyl-l)biphenyl derivatives are further oxidized at the applied potential to bis(pyrazolyl-l)-biphenyl derivatives. 

The first a-cyclopropyl acyl silanes to be isolated were generated by treatment of a,f-unsaturated acyl silanes with diazomethane, followed by vapour-phase pyrolysis of the intermediate pyrazoline derivatives (vide infra, Section IV.D)141. They suffer acid-induced cleavage or rearrangement under more mild conditions than do their carbon analogues146. 

The first recorded cyclopropyl acyl silane (69) was generated by vapour phase pyrolysis of a pyrazoline derived from a,/)-unsaturated acyl silane by 1,3-dipolar cycloaddition of diazomethane (vide supra, Section DTE)141. Exposure of 69 to titanium tetrachloride induced ring expansion to give the cyclobutanone in 75% yield (Scheme 113). 

A stereoselective photochemical addition of diazomethane to unsaturated uronate 40 undergoes a pyrazoline derivative 41 which, after photolysis, leads to cyclopropano-... 

Oxidative processes are very characteristic for pyrazoline derivatives such as dihydroheteroaromatic compounds. However, oxidation of pyrazolines is not a widely used preparative method for the synthesis of the appropriate pyrazoles owing to numerous side reactions following heteroaromatization, and other pathways are usually applied to obtain pyrazoles [66]. It should be noted that pyrazolines unsubstituted at positions 1 and 3 are very unstable compounds and easily decompose in air, with nitrogen elimination. Introducing alkyls or aryls in these positions leads to an increase of their stability but oxidative destruction is also possible, for example, under the action of nitrous acid [116, 117]. 

Reactions of pyrazoline derivatives with electrophilic reagents very often become complicated owing to the oxidative destruction and/or processes related to the C5—Ni bond breaking. 

The formation of pyrazoline derivatives 175 (but not dihydrotetrazolotria-zepines 173, as assumed earlier [53]) is brought about by the condensation of chalcones with diaminotetrazole 172 [128,129]. The structure of the compounds 175 is convincingly verified using X-rays. The mechanism of their formation implies a Dimrothe rearrangement for either the initial diamine or for one of the cyclocondensation intermediates (Scheme 4.51). 

The tertiary and quaternary amine salts of l,3-diphenyl-2-pyrazoline derivatives (Table 7.9) are brilliant, moderately lightfast brighteners for (modified) polyacrylonitriles. Some can also be used to brighten cellulose acetate. Depending on the structure and nature of the anion, concentrated aqueous solutions with long shelf lives can be obtained such products are needed, for example, in gel brightening. 

Other Fibers. The main products used for cellulose acetate or triacetate fibers are pyrazoline derivatives such as 49-51, and for wool typical polyamide brighteners. 

The cycloaddition of diazomethanes under different conditions leads to 3-silyl-l-pyrazoline derivatives in yields variable according to the conditions employed and the substituents on the reactants.106-108... 

Cycloaddition of trimethylsilyldiazomethane with activated olefins leads to pyrazoline derivatives that have the SMA substructure. Two examples are reported in the literature. The first concerns addition to acrylonitrile that gives 5-trimethylsilyl-3-cyano-A2-pyrazoline in good yield.111... 

The second reports the addition to a cyclobutanone derivative that leads to the formation of a A -pyrazoline derivative.112... 

Photolysis of pyrazolines derived from l,2-bis-trimethylsilyl-cyclopropene-3,3-di-carboxylates has also been shown to provide an efficient route to bicyclobutanes 249). 

Generally, the N-N bond may be stabilized toward hydrogenolysis by acetylation or hydrogenation in acetic anhydride, as in eq. 12.72 in the Raney Ni-catalyzed hydrogenation of a pyrazoline derivative at a high temperature and pressure.133 In contrast, 5-methylpyrazoline was hydrogenolyzed to give butane-1,3-diamine in 67% yield under even milder conditions (eq. 12.73).134... 

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