Aryl derivatives hydrazones

Methyl or ethyl chloroformate (70 mmol) was added dropwise to a stirred solution of a hydrazone derivative (60 mmol) of 2-amino-5-chlorobcnzophenone in a mixture of CIICI, (200 mL) and pyridine (15 mL) at 10 C. The mixture was left overnight and treated with a further amount of the alkyl chloroformate (40 mmol) and stirred at 20 C for 2 h. If /V-aryl-substituted hydrazones were used, the mixture was refluxed for 3-6 h. The mixture was poured into ice-water and the organic layer was washed successively with H2Oand 10% aq NaH0O3, dried (MgSO ) and evaporated in vacuo to yield 7 or 8 or a mixture of the two. 

The reaction of hydrazones with elemental fluorine can also be used for the synthesis of gem-in ally difiuorinated compounds (Table 4). The procedure, however, can have severe limitations it is only applicable to aryl ketone hydrazones (no reaction is observed with the hydrazones of benzaldehyde, cyclohexanone, or cyclopentanone), and mixtures ofdi- and monolluorinated compounds are obtained. In some cases, monofiuorinated derivatives are the only reaction products (entries 4 and 5). 

The synthesis of pyridazine derivatives from hydrazones includes the thermal cyclization of 2-arylhydrazono-3-oxo-5-phenyl-4-pentenenitriles (readily obtained from ethyl cinnamate by condensation with acetonitrile followed by Japp-Klingemann type reactions) to l-aryl-3-cyano-6-phenyl-5,6-dihydro-4(l//)-pyridazinones (Scheme 85) <86JHC93>, and base-induced cyclization of a hydrazone of a 4-chloro-l-arylbutan-l-one to prepare a 2,3,4,5-tetrahydropyridazine (Scheme 85) <88JHC1543>. An earlier route to 6-carboxy-5-hydroxy-2-phenyl-3(2//)-pyridazinone via condensation of benzenediazonium chloride and dimethyl acetonedicarboxylate has been adapted to give a series of aryl derivatives either as esters (by thermal cyclization) or as acids (by cyclization with hydroxide). Both cyclizations proceed in high overall yield (Scheme 86) and decarboxylation of the acids also proceeds in high yield <89JHC169>. 

Oxatriazines. (1) Reaction of benzonitrile oxides with hydrazones (Equation 16) - this method gives 3-aryl derivatives (2) reaction of benzonitrile oxides with hydrazine carboxylates and cyclization (Scheme 33) (3) cyclic carbonylation of l,4-disubstituted-4-hydroxy-semicarbazides with (thio)phosgene (Scheme 41) - this method gives 3,6-dione-type derivatives. Methods (1) and (3) both appear quite general and high yielding, with precursors readily available. 

Addition of the formaldehyde-derived hydrazone Bu NHN=CH2 to RCH=CHN02 (R = alkyl, aryl, heteroaryl), catalysed by bis-thiourea (375), has been reported to afford (376) with <72% ee ... 

This problem can be surmounted by the use of BTBSH, which affords the (V-silyl hydrazones cleanly and in high yield (eq 3). Thus, iV-silylated aryl and alkyl hydrazones are prepared hy reaction of l,2-bis(t-butyldimethylsilyl)hydrazine with an aldehyde or ketone in the presence of a catalytic amount of Sc(OTf)3 in dichloromethane (eq 3). A number of Lewis acid catalysts were explored, with Sc(OTf)3 being the most effective, giving the hydrazones in yields of up to 95% as mixtures of the syn- and anti-isomers. In the absence of Lewis acid catalysis, the reaction does not proceed. Unlike the simple hydrazine-derived hydrazones, the resulting iV-silyl hydrazones are stable, isolable, and capable of being stored for extended periods of time. 

Anomalous Fischer cyclizations are observed with certain c-substituted aryl-hydrazones, especially 2-alkoxy derivatives[l]. The products which are formed can generally be accounted for by an intermediate which w ould be formed by (ip50-substitution during the sigmatropic rearrangement step. Nucleophiles from the reaction medium, e.g. Cl or the solvent, are introduced at the 5-and/or 6-position of the indole ring. Even carbon nucleophiles, e.g. ethyl acetoacelate, can be incorporated if added to the reaction solution[2]. The use of 2-tosyloxy or 2-trifluoromethanesulfonyloxy derivatives has been found to avoid this complication and has proved useful in the preparation of 7-oxygen-ated indoles[3]. 

Ethynyl derivatives of 2-aryl-4,5,6,7-tetrahydroindazole were prepared from the p-chlorophenyl hydrazone of cyclohexanone. The hydrazone was treated with two equivalents of -butyllithium at —78°C to generate the dianion, which was then quenched with the appropriate substituted ethyl ester (94MT29). 

Treated with thionyl chloride, hydrazones 490 (R1 = H, R2 = aryl) undergo cyclocondensation to thiadiazoles 506 whereas from aliphatic derivatives 490 (R1 = H, R2 = alkyl), mixtures of thiadiazoles 507 and 508 are formed... 

Watanabe reports a new method for the direct conversion of o-choroacetaldehyde N,N-disubstituted hydrazones into 1-aminoindole derivatives 93 by palladium-catalyzed intramolecular ring closure of 92 in the presence of P Bu3 or the bisferrocenyl ligand 94 <00AG(E)2501>. When X = Cl, this cyclizative process can be coupled with other Pd-catalyzed processes with nucleophilic reagents (e.g., amines, azoles, aryl boronic acids) so as to furnish indole derivatives with substituents on the carbocyclic ring. 

Several approaches to the 1,2,3-triazole core have been published in 2000. Iodobenzene diacetate-mediated oxidation of hydrazones 152 led to fused 1,2,3-triazoloheterocycles 153 <00SC417>. Treatment of oxazolone 154 with iso-pentyl nitrite in the presence of acetic acid gave 1,2,3-triazole 155, a precursor to 3-(W-l,2,3-triazolyl)-substituted a,P-unsaturated a amino acid derivatives <00SC2863>. Aroyl-substituted ketene aminals 156 reacted with aryl azides to provide polysubstituted 1,23-triazoles 157 <00HC387>. 2-Aryl-2T/,4/f-imidazo[43-d][l,2,3]triazoles 159 were prepared from the reaction of triethyl AM-ethyl-2-methyl-4-nitro-l//-imidazol-5-yl phosphoramidate (158) with aryl isocyanates <00TL9889>. 

Alkyl- and aryl-hydrazones of aldehydes and ketones readily peroxidise in solution and rearrange to azo hydroperoxides [1], some of which are explosively unstable [2], Dry samples of the p-bromo- and p-fluoro-hydroperoxybenzylazobenzenes, prepared by oxygenation of benzene solutions of the phenylhydrazones, exploded while on filter paper in the dark, initiated by vibration of the table or tapping the paper. Samples were later stored moist with benzene at —60°C to prevent explosion [3], A series of a-phenylazo hydroperoxides derived from the phenyl-or p-bromophcnyl-hydrazones of acetone, acetophenone or cyclohexanone, and useful for epoxidation of alkenes, are all explosive [4], The stability of several substituted phenylazo hydroperoxides was found to be strongly controlled by novel substituent effects [5],... 

Zinc chloride-doped natural phosphate was shown to have catalytic behavior in the 1,3-dipolar cycloadditions of nucleoside acetylenes with azides to form triazolonucleosides <99SC1057>. A soluble polymer-supported 1,3-dipolar cycloaddition of carbohydrate-derived 1,2,3-triazoles has been reported <99H(51)1807>. 2-Styrylchromones and sodium azide were employed in the synthesis of 4(5)-aryl-5(4)-(2-chromonyl)-1,2,3-triazoles <99H(51)481>. Lead(IV) acetate oxidation of mixed bis-aroyl hydrazones of biacetyl led to l-(a-aroyloxyarylideneamino)-3,5-dimethyl-l,2,3-triazoles <99H(51)599>. Reaction of 1-amino-3-methylbenzimidazolium chloride with lead(fV) acetate afforded l-methyl-l/f-benzotriazole <99BML961>. Hydrogenation reactions of some [l,2,3]triazolo[l,5-a]pyridines, [l,2,3]triazolo[l,5-a]quinolines, and [l,2,3]triazolo[l,5-a]isoquinolines were studied <99T12881>. 

Furthermore, direct halogenation sometimes leads to substitution in the C-residue of the aldehyde hydrazone. For example, hydrazonoyl bromide 28c was obtained by direct bromination of hydrazone 58a or 58b (75CJC1484). Electron-withdrawing substituents in the N-aryl moiety of the arylhydrazone derivatives of heterocyclic aldehydes inhibit ring bromi-... 

The allylation of hydrazones derived from arylalkyl ketones [42] and of N-aryl aldimines in DMF at 0 °C [46] have also been reported. 

Treatment of dehydro-L-ascorbic acid (72) with phenyl hydrazine followed by hydroxylamine yielded the hydrazone oxime (73a), cyclization of which in refluxing acetic anhydride gave 4-[l-//u< o-2,3-diacetoxy-(l-hydroxypropyl)]-2-phenyl-l,2,3-triazole-5-carboxylic acid lactone (74a) <77CAR(59)141>. Analogous reactions of the derivatives (72) with substituted aryl hydrazines yielded the triazoles (74b-d). Alternatively, the hydrazone oximes (73a-d) may be treated with HBr in... 

A convenient synthesis of 1,2,3-thiadiazoles starts with the thioanilide derivative 544, which is converted into the hydrazone 545. Oxidative heterocyclization by treatment with hydrogen peroxide gives exclusively the 1,2,3-thiadiazoline 546 (Scheme 245) <2003S2559>. This method has been extended to include arylhydrazono thioacetamides, such as 547, which undergo oxidative cyclization using bromine to afford 2-aryl-l,2,3-thiadiazol-5(2//)imines 543 (Scheme 246) <2004RJ0818, CHEC-III(5.07.9.5)482>. 

Intramolecular insertion of olefins and acetylenes into the Zr-C bonds of zirconaaziridines can lead to annulation reactions. Livinghouse showed that alkyl-, silyl-, and aryl-substituted C-C multiple bonds readily insert into the Zr-C bonds of zirconaaziridines derived from the hydrazones 28 and 29, yielding cyclic products [28]. 

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