Hydrazones reaction with lead

Enantiomerically pure nitrile imines (211) have also been generated by the lead tetraacetate oxidation of aldehydo sugar p-nitrophenyl hydrazones. Reaction with methyl acrylate gave the pyrazolines as a 1 1 mixture of the (55) and (5R) epimers, which were resolvable in some cases (116). 

Reaction of tosyl hydrazone 1 with a strong base initially leads to a diazo compound 3, which in some cases can be isolated ... 

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>. 

A novel hydrazepine formation is observed in the iridium-catalyzed reaction of alkynyl hydrazone 304 with Bu Me2SiH in excess under slightly forcing conditions (Equation (53))/ The transformation leading to 305 can be explained by continuous interaction of Bu MceSiH with a silylformylation product of 304 under the reaction conditions/ ... 

Ethoxycarbonyl hydrazones are also used for the reaction with Se02/AcOH leading to 1,2,3-selenadiazoles. The reaction of hydrazone 261 with Se02/AcOH at room temperature gave the probable intermediate 262 toward 1,2,3-selenadiazole in 69% yield (Equation 32) <2004MOL957>. 

In contrast to the cycloaddition reaction of furan with hydrazones leading to furo[2,3-c]py-ridazines <91T5615>, the /1-chloroazo alkene (204) undergoes a [4 + 2] cycloaddition reaction with... 

Examples include the synthesis of 3-amino-l,2,4-oxadiazoles starting from 3-acylamino-5-methyl-l,2,4-oxadiazole <2002H811> and 2-aryl-l,2,3-triazoles from l,2,4-oxadiazole-3-ketone arylhydrazones <1999T12885, 2006JOC5616>. Oximes, hydrazones, formamidines, and thioureas of the furazan series also undergo base-catalyzed mononuclear rearrangements <2004RCB1121>. Nucleophilic attack at N(3) takes place in the benzofuroxan series. For example, reaction with secondary amines leads to o-nitroarylhydrazines (Scheme 55). 

Oxidative processes using mild oxidants (e.g., HgO or Mn02) leading to NN bond formation convert /k-hydrazones 538 into the 1-amino-l,2,3-triazole derivatives 539 (Scheme 242) <1967TL3295, 1971JPR882>. A regioselective synthesis of 2,4-disubstituted 1,2,3-triazoles is based on a reaction of aminoacetophenones 540 with hydrazines (Scheme 243) . The reaction with methylhydrazine proceeds well without any catalysis, but that with phenylhydrazine requires cupric chloride as a catalyst. It is assumed that hydrazone 541 that forms in the first step is in a tautomeric equilibrium with its azo form 542 <2003SC3513>. 

Annelation of steroidal dienamines with substituted phenacyl bromides (7 examples) or with benzenediazonium salts (11 examples) has been shown to lead to the corresponding furano- and indolo-steroids.89 Thus the A3,5-dienamine derived from A4-androstene-3,17-dione reacted with p-bromophenacyl bromide to yield the A5-androstano[3,4-h]furan (199) in 26% yield, and reaction of the same A3,5-dienamine with benzenediazonium fluoroborate at -45 °C led to formation of the hydrazone (200) which underwent Fischer-indole cyclization on treatment with phosphorus oxychloride to produce the A4-androstano[6,7-6]indole (201). The A3,5-dienamine derived from 17/3-acetoxyandrost-4-en-3-one has been converted into the benz[4,5,6]-steroid (202 R1 = Me, R2 = H) by reaction with methyl vinyl ketone and into the analogous benzsteroid (202 R1 = H, R2 = Me) on treatment with crotonal-dehyde.90 A route to the condensed pyrroline ring system (203) has been devised... 

Oximes, hydrazones, semicarbazones, diazines and carbodiimides all undergo reactions involving addition to a carbon-nitrogen double bond (A, D], but these reactions are of limited value, with the exception of the reaction with ketoximes. This last reaction, with an excess of Grignard at elevated temperatures, is a useful route to aziridines, (4), although yields are rarely high. In some cases, reduction of the intermediate azirine (2) leads to an alternative aziridine (5). 

Isatin hydrazones and thiosemicarbazones can also be used as substrates for the Mannich reaction, leading to functionalization at N- . Isatin-3-hydrazone reacts with 1,1-... 

Just as primary aromatic amines replace the CH3S group of the isotrithionium salts (259) to form protonated anils or hydrazones (261), the reaction with aliphatic amines such as piperidine or morpholine leads to 303. 

The intermediate l-aza-2-azoniallene cations can undergo 1,3-dipolar cycloaddition reactions with inverse electron demand [119]. Thus, oxidation of a A -phenyl hydrazone in the presence of pyridine leads to the formation of a. y-triazolo[4,3-a]-pyridinium salt by attack of pyridine as a nucleophile on the intermediate nitrilimine [Eq. (17)] [120]. Other examples are reported by Jugelt [121]. 

For the preparation of hydrazones, Schonberg " recommends that equivalent amounts of the ketone and hydrazine be refluxed in -butanol (b.p. 117.7°) for 2 hrs. Use of ethanol requires a longer reflux period and use of ethylene or propylene glycol may lead to side reactions. Thus on applying the glycol procedure for conversion of fluorenone to the hydrazone, Baltzly et al. observed formation of considerable fluorene (interference by an unusually facile Wolff-Kishner reaction). On refluxing the reactants in n-butanol for 4 hrs., the hydrazone was obtained in 67% yield. However, a superior method for the preparation of hydrazones involves reaction of the ketone with N,N-dimethylhydrazine which see) followed by an exchange reaction with hydrazine. 

The outcome of the reaction of hydrazones with lead tetraacetate is dependent upon the nature of the hydrazone and the reaction conditions. Mechanistically, the reaction was first suggested to imply the formation of a pair of free radicals, Pb(0Ac)3 and the hydrazonyl radical. However, ESR studies failed to detect the presence of radicals in solutions of hydrazones and lead tetraacetate. The reaction was explained by a two step mechanism, involving first the formation of a covalent hydrazone-lead intermediate followed by an intramolecular rearrangement leading to the a-acetoxy products which can then evolve into different derivatives. ... 

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