2-Hydrazono-5- substituted

Isopropylidene and benzylidene hydrazones of the selenazoles w hich are unsubstituted in the 5-position react with p-nitrosodiethyl-and p-nitrosodimethyl-aniline in organic solvents on heating and the addition of acetic acid or pyridine. - Thus result crystalline, deeply colored, 2-hydrazono-5-(p-dialkylaminophenylimino)selenazoles (correspondingly substituted in the 4-position), details are given in Table VII. The presence of an aromatic residue in the 4-position of the selenazole ring appears to be needed to obtain crystalline compounds. 

The susceptibility of the sydnone ring to acid-catalyzed hydrolysis at elevated temperature is exploited for the preparation of hydrazines <2000MI227>. Primary amines are first converted to sydnones, which are then hydrolyzed to give hydrazines that may be isolated or reacted further without isolation <1996CHEC-II(4)165>. As masked hydrazines, 3-arylsydnones are firstly subjected to acid-catalyzed ring opening and then allowed to react further in situ with 2-(4-chlorophenyl)hydrazono-3-oxo-butyric acid to form substituted pyrazolidinones (Equation 2) <2005SC2169>. 

Substituted 1,2,3-triazoles are oxidized by w-chloroperoxybenzoic acid at the more basic N(3) to give the corresponding triazole A -oxides. The yield is lower if an electron-withdrawing substituent is present at the C(4) or C(5) position <87ACS(B)724>. 2-Alkyl-1,2,3-triazole-1-oxides are produced from the oxidative cyclization of alkyl hydrazono oximes <86ACS(B)262> see Section 4.01.8.1. 

Amino-1,2,3-triazoles with a substituent at the 4-position have been prepared (i) from azides and active methylene nitriles (ii) from azides and ynamines (iii) from diazomethane and carbo-diimides (iv) from azides and 1,1-diaminoethenes and (v) from the rearrangement of 3-hydrazono-1,2,4-oxadiazoles. Among these, the first method, a regiospecific process, is the most versatile and convenient although it is suitable only for 5-NH2-substituted triazoles. Other methods are used to prepare 5-NHR , 5-NR R - and 5-NHCOR-substituted triazoles. Intramolecular cyclization of suitable precursors also gives 5-aminotriazoles. For example, a-imino-a-piperidyl phenylhydrazones (838), in the presence of copper acetate, give 5-piperidyl-triazoles (839) (Equation (85)) <94H(38)739>. 

The products obtained in the reaction of A -cyclopropyl-4,5-difluoroanthranilic acid hydrazides 429 with triphosgene were dependent on the steric hindrance imposed by substituent R at position 3, and not the electronic effect of this group. While the unsubstituted compound 429 (R = H) gave exclusively the 4-hydrazono-3,l-benzoxazin-2-one-type product 430, the similar reactions of the chloro-, methyl-, and methoxy-substituted analogs 429 (R = Cl, Me, OMe) resulted in formation of the corresponding quinazoline-2,4-diones 431 as the sole products. For the fluoro-substituted compound 429 (R = F), a 20 80 mixture of the products 430 and 431 was obtained (Equation 46) <2005JHC669>. 

The reaction of 1,2-dicarbonyl compounds (452) with amidrazones (453) is the best method for the synthesis of alkyl, aryl or hetaryl substituted 1,2,4-triazines (78HC(33)189, p. 195). No limitation of this synthetic principle is reported, except that it is, of course, preferable for the dione (452) to be symmetrical. The best reaction procedure is to add the dicarbonyl compound to a solution of the free amidrazone, or amidrazonium salt in the presence of one mole of base, and allow a reaction time of about 12 h. Since the first step of this reaction, i.e. condensation of the hydrazono group with one carbonyl group, is fast, while the second, i.e. condensation of the amide group with the other carbonyl, is slow, the intermediate (454) has been isolated in a few cases. This method has been used also for the synthesis of compounds containing more than one 1,2,4-triazine nucleus, and for the parent 1,2,4-triazine (1) (68CB3952). 

Typical preparations have been described for 2-(r-hydroxyiminomethyl)pyrazine (138) 2-(4 -dimethylamino-T-hydroxyiminobutyl)pyrazine (1186) 2-(2 -hydroxy-iminopentyl)-6-methylpyrazine (645) 2-(2 -hydroxyimino-3, 3 -dimethylbutyl)-6-methylpyrazine (645) 2-[r-hydroxyimino-2-(pyridin-2"-yl) (hyl]pyrazine (642) 2-[2 -hydroxyimino-2 -(pyridin-2"-yl, pyrazin-2"-yl, or pyrimidin-4 -yl)ethyl]pyrazine (642) 2-[l, 2 -bishydroxyimino-2 -(pyridin-2"-yl)ethyl]pyrazine (642) 2-12 -(2",4"-dinitrophenylhydrazono)-3 -methylbutyl]-6-methylpyrazine (645) 2-[ 1-(substituted hydrazono)ethyl]pyrazine (1196) 2-[l -phenyl-1 -(substituted hydrazono)methyl]-pyrazine (1196) 2-(r-thiosemicarbazonoethyl)pyrazine (138) 2-(2 -chloro-l -thiosemicarbazonoethyOpyrazine (138) and 2,5-dimethyl-3,6-bis(r-semicarbazono-ethyl)pyrazine (1196). 

I. Of 2-[(3-oxopyrazol-4-yl)hydrazono]malonic Acid Esters or Substituted Acetonitriles... 

Isocyanates react at ambient temperature with a hydrazono-iminophosphorane to yield a 7-substituted aminotriazolo compound. The initial reaction is probably between the isocyanate and the iminophosphorane to form a carbodi-imide. Heat is needed to induce a hydrazono-iminophosphorane to react with benzoyl chloride and to form a new triazole ring, but the yields are then usually high. 

By the cyclization of hydrazones. A common characteristic of hydrazone cyclizations is the requirement of high temperatures when no solvents are used. Under these conditions, heating 3-[(Z)-2-(f-butyl-substituted silyl)hydrazono]butanoates 71a-c at 200 °C initially formed pyrazol-3-ones 72a-c which were not stable at that temperature but underwent a l,3-N,0-silyl group migration to the O-silylpyrazoles 73a-c (99JOM341) (Scheme 18). 

Thiadiadiazines are prepared best by condensation of thiohydrazides with a-halocarbonyl compounds. As thiohydrazide components, most substituted thiosemicarbazides, aryl and alkyl thiocarbonylhydrazides, or 0-alkyl dithiocarbazates can be used. The cyclocondensation with thiosemicarbazides and a-halocarbonyl compounds can provide three isomeric compounds, 2-amino-l,3,4-thiadiazines A, 2-hydrazino-l,3-thiazoles or 2-hydrazono-2,3-dihy-dro-l,3-thiazoles B, and 2-alkyl(aryl)imino-3-amino-2,3-dihydro-l,3-thiazoles C (Scheme 31). The course of the cyclization of thiosemicarbazides with a-halocarbonyl compounds depends on the acidity of the reaction medium and the substituents R, R, and R. The reaction of aromatic a-halo ketones with thiosemicarbazides leads under neutral... 

Gomha and Khalil (2012) developed a successful application of ultrasound irradiation for the rapid synthesis of a novel series of 3-[l-(4-substituted-5-(aryldiazenyl) thiazol-2-yl)hydrazono)ethyl]-2//-chromen-2-ones (48) in good yields (72%-76%), via reactions of 2-(l-(2-oxo-2//-chromen-3-yl)ethylidene)thiosemicarbazide (47) and hydrazonoyl halides (39) in dioxane in the presence of a catalytic amount of... 

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