Hydrazones tetraacetate

Lead tetraacetate is often used as the oxidizing agent for the conversion of hydrazones into ring-fused systems. 

Another example of this rearrangement has been used to prepare 1,2,3-triazole 146 from furazanic phenylhydrazone 147 (Scheme 84) [93JCS(P1)2491]. Interestingly, furoxanic Z-phenylhydrazones 150 underwent thermal recyclization to 1,2,3-triazole A-oxides 152, evidently through intermediate 151. Treatment of the hydrazone 150 with rerr-BuOK leads to the nitromethyl derivative 149 [OOOMIl] (Scheme 84). Lead tetraacetate oxidation of 147 with subsequent Lewis acid treatment of the initially formed intermediate afforded indazole 148 (Scheme 84) (85JHC29). 

Lead tetraacetate has been used to convert phenols, with a hydrazone group in the ortho position, to carboxylic esters, for example. 

When hydrazones are oxidized with HgO, Ag20, Mn02, lead tetraacetate, or certain other oxidizing agents, diazo compounds are obtained ... 

Lead tetraacetate, oxidation of a hydrazone to a diazo compound, 50, 7 Lithio ethyl acetate, 53, 67 Lithium, reductions in amine solvents, 50, 89 Lithium aluminum hydride, reduction of exo-3,4-dichloro-bicyclo-[3.2.l]oct-2-ene to 3-chlorobicyclo[3.2.l]oct-2-ene, 51, 61... 

The mixed hydrazones (667), prepared from diacetyl monobenzoyl hydrazone and arylhydrazines, undergo oxidative cyclization to 2-aryl-jV-benzoyl-4,5-dimethyl-l,2,3-triazol-l-ylimines (668) in 32-76% yield upon treatment with lead tetraacetate in acetonitrile (Scheme 132) <92JOC2252>. The cychzation of bishydrazones to 1,2,3-triazoles can also occur in acidic or basic media. For instance, the tetrahydrobenzo[ /]triazol-4-one (669) is prepared by the base-catalyzed cyclization of the corresponding a-hydrazono oxime (Equation (53)) <85HCA1748>. 3-Methyl-1,2-cyclohexanedione reacts... 

The lithiated hydrazone (130) reacts with the salt (131) to give the amidrazone (132) in 35% yield. Oxidation of (132) with lead tetraacetate gives the 3,4-dihydrotriazole (133) (Scheme 26) <86CC1721 >. 

The carbonyl ylide precursor can be generated by lead tetraacetate oxidation of the hydrazone 58. Thermolysis of 59 in the presence of perdeuterated acetone led to a variety of products, some of which are shown above. An internal quench of the ylide via a 1,4-proton migration led to enol ether 61, while cycloaddition with perdeuterated acetone formed the dioxolane 62 and its regioisomer. Interestingly, the presence of products such as acetone and propene-t/s are proposed to indicate a reversible fragmentation of the ylide to a carbonyl derivative and a carbene. 

The oxidation of hydrazones 143 provides, in principle, a very convenient route to nitrile imines from easily accessible starting materials. However, the earliest reagent used, lead tetraacetate, was of limited effectiveness as yields were low and the reaction often gave high yields of diacyUiydrazides as byproducts. Work has been done on the apphcation of several other oxidants to this process to produce a more effective general route. The one that has proved most popular is chloramine T (A(-chloro-A(-sodio-p-toluenesulfonamide, CAT) which is used under mild conditions and has been shown to work well for both cycloaddition (79) (e.g., in the preparation of 146 from 145) and electrocychzation (80) reactions. 

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). 

Acyclic sugar hydrazones react with benzenediazonium chloride to give red formazans. When oxidized with N-bromosuccinimide (or, after acetylation, with lead tetraacetate), these yield tetrazolium salts. 

The oxidation of hydrazine derivatives with diethyl azodicarboxylate is of particular interest because it involves direct hydrogen abstraction. The oxidation of keto hydrazones with lead tetraacetate leads to azoacetates, presumably by a free radical mechanism. 

However, with lead tetraacetate, keto hydrazones may be oxidized to azoacetates according to Eq. (44) [102]. 

The reaction of aldehyde hydrazones is more complex and requires further study [103]. It is usually carried out with a 90% solution of lead tetraacetate in acetic acid with sufficient additional solvent to bring about homogeneous reaction conditions initially. 

If an N-substituted hydrazone is used, a quaternary triazolopyridinium salt (13) is the product. Such oxidations have been performed with lead tetraacetate,15 with A/-bromosuccinimide,16 or electrochemically.17... 

Oxidation of 2-azidophenyl ketone hydrazones (455) affords the 2-azidophenyldiazoalkanes (456) which can be cyclized thermally to 1,2,3-benzotriazines (457) (75JCS(Pl)3l). Similarly, 2-aminophenyl ketone hydrazones (458) give 1,2,3-benzotriazines (457) on oxidation with lead tetraacetate (75JCS(Pl)3l). 

Cyclization of the hydrazone 571 by the action of lead tetraacetate in benzene afforded the triazolo[4,3-c]pyrimidine 572 (57JCS727) (Scheme 112). 

The aldehyde from the hydrolysis of 25 proved to be difficult to isolate but could be converted directly to the hydrazone 26, whose oxidation with lead tetraacetate gave the l,2,3-triazolo[l,5-c]pyrimidine 27 (78JHC1041). 

Hydrazino nitrogen heterocycles are readily converted into 1,2,4-triazolo[/ ]-fused systems, as exemplified by Scheme 54 <1971JOC10>. A similar approach has been used for the synthesis of triazoloindole derivative 91 (Scheme 55) <2005BMC1847, CHEC-III(11.03.9.1)117>. Oxidation of the 2-pyrazolyl hydrazones 92 with lead tetraacetate gives, via azines 93, the 3//-pyrazolo [5,12,-4-triazoles 94 (Scheme 56) <1979TL1567>. 

Lead tetraacetate converts hydrazones to carbonyl compounds plus the corresponding alcohols. For example, benzophenone hydrazone is converted into benzophenone in 36-67% yields plus lesser amounts of benzhydrol. Substituted ketone hydrazones give a-acetoxyazo compounds with 1 equiv. of lead tetraacetate,aldiough 2 equiv. of lead tetraacetate results in ketones. This also has been observed with tosylhydiazones. Aiylhydiazones of aldehydes give diacylhydrazines (equation... 

Azodicarboxylates undergo Michael addition to the electron-rich 5-position. The intermediate hydrazino ester is converted with bases to fervenu-lones or converted with Vilsmeier reagent (POCl3-DMF) to fervenulins, which are available by oxidation of the corresponding hydrazone using lead tetraacetate [75JOC2321 76JCS(P 1)2398] (Scheme 82). 

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