Hydrazines, aromatic

Aromatic Hydrazines. A general synthesis for aryUiydraziaes is via diazotization of aromatic amines, followed by reduction of the resulting diazonium salt (18) ... 

Hydrazines and compounds that can be hydrogenated to hydrazines undergo N-N bond rupture on noble metal catalysts. Pd seems to be the best catalyst for the hydrogenolysis of the N-N bonds in aromatic hydrazines, whereas Rh seems best for the aliphatic ones. Ni is also useful for the hydrogenolysis of N-N bonds in hydrazines. 

Fluorinated triazole derivatives have been prepared by a somewhat deceptive route that starts with imine perfluoro(5-aza-4-nonene) 140 reaction of 140 with aromatic hydrazines gives 1,2,4-triazoles 141a-g in good yields (Equation 44 and Table 27) <2001RJ01621, 2001ZOR1693>. 

Table 27 Reaction of perfluoro(5-aza-4-nonene) with aromatic hydrazines (Equation 44)... 

Aromatic hydrazines, 13 573 Aromatic hydrocarbons, 18 593 biodegradability of, 25 826 composition of, 25 168 as diluents, 10 430 fluorinated, 11 866 nitration of, 17 161 separation of, 10 782-785 as solvents for poly(ethylene oxide),... 

If the hydroformylation of olefins is conducted in the presence of aromatic hydrazines and Bronsted or Lewis acids indoles can be obtained directly in one pot [91-93,95]. Hydroformylation of the olefin gives an intermediate aldehyde, which is trapped immediately by the present aromatic hydrazine as an aromatic hydrazones similar to the formation of imines under hydroformylation conditions. Under acid mediation these aromatic hydrazones undergo a Fischer indolization, consisting of a [3,3]-sigmatropic rearrangement followed by a cyclization and elimination of ammonia (Scheme 38). 

General Procedure for the Hydroformylation/Fischer Indole Synthesis. Synthesis of Tryptamine Derivatives in Water. Aminoolefin (1 eq), aromatic hydrazine (1 eq), Rh(acac)(CO)2 (0.3 mol %) and TPPTS (1.5 mol %) are dissolved in H2SO4 (4wt% in H2O, 2.5 wt % olefin), filled in an autoclave and pressurized with lObar H2 and 50 bar CO. After stirring for 3 days at 100 °C ammonia (30 wt% in water) is added and the mixture is extracted with EtOAc. The solvent is evaporated to give the product which purified by column chromatography (silica, CH2C12, PrOH, NEt3) if necessary. 

T1 resin traceless linker [131-134], synthesis of phenols [135], biaryls, alkyl arenes [136, 137], azides [138], aromatic hydrazines, halides [cf. 128, 129, 139], ester, azo compounds, cinno-lines [140], benzotriazoles [141]... 

Aromatic hydrazines 542, azo compounds 543 or azoxy compounds 544 were reduced using the NiCl2-2H20/Li/DTBB (10%) combination in THE at room temperature to yield the corresponding aromatic amines 545 in 57-88% yield °. 

Examples of synthesis of five-membered heterocycles following this strategy are limited in number. An approach to 1,3,4-triazoles involves bonding of C-l and C-3 of vinyl isocyanate 150 to both nitrogen atoms of aromatic hydrazines (78JOC402) (Scheme 37). The reaction was run at room temperature and gave quantitatively regioisomer 151 or a mixture of 151 and 152 when p-nitrophenyl and phenylhydrazine, respectively, were employed. 

Isothiocyanates react with substituted aromatic hydrazines at low temperature or in acid media to give 2,4-substituted thiosemicarbazides. At elevated temperatures 1,4-thiosemicarbazides are produced [46-48] (Eqs. 14, 15). 

Aromatic hydrazines are best prepared by reduction of aromatic diazonium salts (Table 23-4). 

This reaction appears to be similar to the imidazo-pyridine formation mentioned above, most likely via a [5+1] insertion reaction of the isocyanide into the corresponding hydrazone. This reaction mechanism seems likely since only electron-rich aromatic hydrazines yielded cinnolines. The Ugi 4-CR reaction with phe-nylhydrazine is known and has been reported to give the expected Ugi-type 4-CR product. 

Aromatic hydrazines like hydrazobenzene are readily oxidized to azobenzenes with air in the presence of alkali or by the action of sodium hypobromite. Aliphatic azo compounds are also prepared from the corresponding hydrazo compounds. Thus azomethane, CH5N=NCHj, is jjte-pared by the oxidation of sym-dimethylhydrazine with cupric chloride (70%). The oxidation of -hydrazotoluene, CjHsCHjNHNHCHjCjHs, to the azo compound is accomplished with mercuric oxide in boiling ether (76%). ... 

An important support for this theory is the circumstance that the bodies formed by the action of aromatic hydrazines on quinones are identical with those obtained from phenols and diazo-compounds. Phenylhydrazine, for example, reacts with a-naphthoquinone, producing the same compound which is formed by combination of a-naphthol with diazobenzene [3j. The first method of formation renders the formula... 

Hi) Heterocycles which provide all the ring atoms of isoxazoles Diaroylfuroxans (434) when heated with aniline in ether solution undergo a complicated reaction which leads to 3-anilino-4-nitroso-5-arylisoxazole (435). One of the acyl groups is eliminated in the form of an acylanilide. Aromatic hydrazines and benzylamine can be used instead of aniline (62HC(17)1, p. 35). 

R = Me2C=CH-CH2-CH2) with hydrazine hydrate leads to carbamate intermediates, which undergo cyclization to give 5-hydroxy-5.6-dihydro-4/f-l,3,4-oxadiazin-2(3//)-ones 311. The thermal dehydration of 311 gives 1,3,4-oxadiazin-2(3//)-ones 312 <2003CHE1057>. In contrast to the case with hydrazine hydrate, the reaction of aromatic hydrazines with l,3-dioxolan-2-ones 310 provides 3-arylamino-4-hydroxyoxazolidin-2(3//)-ones 313. 

This reaction was first reported by Fischer and Jourdan in 1883. It is a synthesis of indole derivatives by the treatment of aryl hydrazones coupled from aromatic hydrazines and ketones or aldehydes with either a mineral or Lewis acid. Therefore, it is generally known as the Fischer indole synthesis. In addition, it is also referred to as Fischer cyclization, Fischer indole cyclization, Fischer indole reaction, Fischer indolization, Fischer reaction, and Fischer indole annulation. Although the mechanism has been extensively studied, the one formulated by Robinson and Robinson is now generally accepted. It involves the following steps (a) initial acid-catalyzed tautomerization of an aromatic hydrazone to an ene-hydrazine, b) a [3,3]-sigmatropic rearrangement of ene-hydrazine to a M-imine intermediate, (c) re-aromatization to aniline, d) intramolecular nucleophilic attack to form aminal, and (e) extrusion of an ammonia to afford the indole. 

The reaction is quite effective under thermal conditions for terminal and internal allq nes with a variety of aliphatic and aromatic amines or aromatic hydrazines, giving moderate to good yields. 

A systematic study correlating regiochemistry with the specific reaction conditions and the electronic/steric characteristics of 1,3-diketones and aromatic hydrazines in the synthesis of l,5-diaryl-3-substituted pyrazoles was carried out by Singh et al. Usually, cyclocondensations between arylhydrazines and 1,3-diketones are carried out on polar, protic solvents such as alcohols or acetic acid. However, excellent yields and regioselectivities were obtained in reactions of l-aryIbutane-l,3-diones 11 with arylhydrazine hydrochlorides in iV.iV-dimethylacetamide in the presence of 0.5 equiv of 10 N aqueous hydrochloric acid. Nevertheless, when similar reaction conditions were performed in ethanol under reflux, the regioselectivities were lower (80 20-86 14). 

Many sugars contained in mixtures may be separated and isolated in the form of hydrazones by the addition of first one aromatic hydrazine and then a second. The... 

The reaction products of the reducing sugars and aromatic hydrazines are very useful derivatives for identification purposes. One mole of hydrazine may react to give the sugar hydrazone, or two residues may be intro-... 

With aromatic hydrazines Co(C6HsNHNH2)3Cl2 291 4.96 Gouy octahedral coordination 71S25... 

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