Arylhydrazine

They are formed by treatinga-diketones, a-hyd-roxyaldehydes, hydroxyketones, aminoalde-hydes or aminoketones with arylhydrazines. Sugars can be identified by their osazones which have characteristic melting-points, formation times or crystal appearance. 

HC(22)l). Other azopyrazoles (318) and (319) have been described in Section 4.04.2.1.4(viii). These compounds can be reduced to amines (zinc and acetic acid) or to arylhydrazines (zinc in alkaline medium) (67HC(22)l). 

Owing to their particular interest two individual reactions will now be discussed separately. The reaction of methoxycarbonylhydrazine and 3-bromo-2,4-pentanedione affords, in addition to the expected pyrazole (608), a pyrazolium salt (609), the structure of which was established by X-ray crystallography (74TL1987). Aryldiazonium salts have been used instead of arylhydrazines in the synthesis of pyrazolines (610) and pyrazoles (611) (82JOC81). These compounds are formed by free radical decomposition of diazonium salts by titanium(n) chloride in the presence of a,/3-ethylenic ketones. 

Aniline 77 was converted into its diazonium salt with nitrous acid and this was followed by reduction with stannous chloride to afford the corresponding arylhydrazine 78. Condensation of 78 with 3-cyanopropanal dimethylacetal 79 gave the arylhydrazone 80. Treatment of 80 with PPE resulted in cyclization to indole 81. The nitrile group was then reduced to the primary amine by catalytic hydrogenation. Reaction of the amine with excess formalin and sodium borohydride resulted in Imitrex (82). 

The mechanism of the decarboxylation of isoxazole-3-car boxy lie acids has not yet been specially studied, but the available experimental evidence allows some suggestions to be made. It seems that on heating isoxazole carboxylic acids in solution, or in the presence of arylhydrazines, it is the acid anion (158) formed which is being de-... 

In order to allow further transformation to an indole, the carbonyl compound 8 must contain an a-methylene group. The hydrazone 1 needs not to be isolated. An equimolar mixture of arylhydrazine 7 and aldehyde or ketone 8 may be treated directly under the reaction conditions for the Fischer indole synthesis. ... 

In the hydrogenation, 200 g of acetophenone azine, 1000 ml of EtOAc and 5 g of 10% Pd-on-C was shaken at 30-50 psig for 10 h. Hydrogen absorption had ceased. About 7.6 g of phenylethylamine, formed by cleavage of the N—N bond, was obtained as a by-product. Oxidation of hydrazines can be done catalytically. Ethyl 2-arylhydrazine carboxylates were oxidized easily by bubbling air at 25 "C through a toluene or dioxane solution in the presence of Pd or Pt (5d). 

Hydrazino compounds can react with one or two equivalents of arenediazonium ions. In reactions of arylhydrazines without substituents at the P-nitrogen in mineral acid media the initial product, the 1,4-diaryltetraz-1-ene (6.24), disproportionates rapidly into aryl azide and amine (Scheme 6-17). As shown by 15N labeling experiments (Clusius and Craubner, 1955), equal amounts of all the products shown in Scheme 6-17 are obtained. In acetate buffer the reaction is regiospecifically different. The diazonium ion attacks the a-, not the P-nitrogen, and a 1,3-diaryltetraz-l-ene is formed (6.25). 

Dihydroxybenzene (hydroquinone), and probably also the 1,2-isomer, act as reducing agents for arenediazonium ions arylhydrazines are formed, but not in good yields. The azo coupling of 2-hydroxy-l,4-benzoquinone is discussed in Section 10.10 (Scheme 10-71). 

The vicinal dihydrazones formed from monosaccharides with arylhydrazines have been called arylosazones, but are preferably named as ketoaldose bisfphenylhydra-zone)s... 

Fig. 17 Rapid preparation of imidazoles and thiazoles on solid-phase. Reagents a RNH2, (CH30CH2)2, MW 220°C, 15min, closed vessel b TFA in CH2CI2, rt, 60min. R = aliphatic, benzyl, or arylamines or arylhydrazine...

However, in some cases azines can be converted to hydrazones by treatment with excess hydrazine and NaOH. Arylhydrazines, especially phenyl, p-nitrophenyl, and 2,4-dinitrophenyl, are used much more often and give the corresponding hydrazones with most aldehydes and ketones.Since these are usually solids, they make excellent derivatives and are commonly employed for this purpose. Cyclic hydrazones are also known, ° as are conjugated hydrazones. a-Hydroxy aldehydes and ketones and ot-dicarbonyl compounds give osazones, in which two adjacent carbons have carbon-nitrogen double bonds ... 

Reaction of 6-phenacylimidazo[l,2- ][l,2,4]triazin-7-one, 164, with arylhydrazines gives the corresponding hydra-zones, which are cyclized to imidazopyridazinotriazines 165 upon treatment with phosphorus oxychloride... 

Other non-traditional preparations of 1,2,3-triazoles have been reported. The rearrangement in dioxane/water of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole into (2-aryl-5-phenyl-27/-l,2,3-triazol-4-yl)ureas was investigated mechanistically in terms of substituents on different pathways <06JOC5616>. A general and efficient method for the preparation of 2,4-diary 1-1,2,3-triazoles 140 from a-hydroxyacetophenones 139 and arylhydrazines is reported <06SC2461>. 5-Alkylamino-] //-], 2,3-triazoles were obtained by base-mediated cleavage of cycloadducts of azides to cyclic ketene acetals <06S1943>. Oxidation of N-... 

JOC8210>. Condensation of succinaldehyde with arylhydrazines and benzotriazole gives 1-aminopyrrolidines 646 that upon treatment with organomagnesium reagents rearrange to 1,4,5,6-tetrahydropyridazines 647 <1998S1627>. 

NHNH2-------- —A, .2 This salt converts arylhydrazines at low temperatures... 

Aryl chlorothioformates, 23 628 Aryl complexes, zirconium, 26 655 Aryl ethers, uses for, 70 581 2-Arylglycine esters, 72 166 Aryl halide amination, 9 278 Aryl halides, reaction with carbon monoxide, 5 11 Arylhydrazines, 9 270 Arylmethane dyes, 9 503... 

The l-arylpyrazol-5-ones (4.9), prepared by the two-step condensation of an arylhydrazine with ethyl acetoacetate, are the most commonly used coupling components for the synthesis of greenish yellow azo dyes. Coupling occurs at the 4-position of the pyrazolone ring which, as in the case of the acetoacetarylamides discussed above, is activated towards electrophilic attack by the two flanking unsaturated carbon atoms (Scheme 4.14). 

Closely related to the pyrazolones, but less commonly used, are the 5-aminopyrazoles (4.10). Again, these compounds give greenish yellow dyes when coupled at the activated 4-position indicated by the arrow in Scheme 4.15. The aminopyrazoles are prepared by condensation of an arylhydrazine with 3-aminobut-2-enenitrile (diacetonitrile), which is itself produced by dimerisation of ethanenitrile (acetonitrile) over a nickel catalyst. 

The method of Y. Meyer, reduction of the diazonium chlorides to arylhydrazines with strongly acid stannous chloride solution, is less elegant. The difference in the actions of stannous salt in acid and in alkaline solution should be noted. 

Arylhydrazines were reacted with EMME at ambient temperature for 24 hr to give hydrazinomethylenemalonates (87GEP33617554). 

TosN, (0.37 g, 2 mmol), the arylhydrazine (2 mmol), and TEA-Br (0.1 g, 0.5 mmol) in xylene (10 ml) are added to aqueous NaOH (50%, 10 ml) and the mixture is refluxed until the azide has been fully consumed (2-10 h). The organic phase is separated and the aqueous phase is extracted with PhH (3 x 10 ml). The combined organic solutions are dried (MgS04) and evaporated to yield the arene [e.g. PhH 40% (6 h) pyridine 98% (6 h) from 2-hydrazino derivative pyridazine 79% (8 h) from 3-hydrazino derivative)]. 

The electrochemical oxidation of A, Ai-dibenzyl, Ai -arylhydrazines gives carbocations that react with alkenes affording five-membered heterocycles (Scheme 48) [70]. 

Photo-oxidation of l,l-dialkyl-2-arylhydrazines by single-electron transfer with trimethylsilyl cyanide (TMSCN) as cyanide ion source leads to regio- and stereoselective a-hydrazino nitriles. This stereoselective cyanation of hydrazines takes place on the more substituted carbon atom compared with the results obtained with tertiary amines (Scheme 5). 

In the reflux procedure, minor amounts of the corresponding arylhydrazines are formed as by-products. 

The oxidation of arylhydrazines with An2TeO is unsuitable for synthetic purposes, since it furnishes a complex mixture of products. 

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