Bishydrazone oxidation

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 bishydrazones of the 1,2-diketones from inositols have also been converted into triazoles.222,223 The conversion of arylosazones into the corresponding osotriazoles requires the presence of an oxidant, and it is obvious that simple removal of aniline from the osazone, as suggested by the equation, is not involved. In addition to copper(II) sulfate, the reagent most commonly used, other oxidizing heavy-metal salts, such as ferric sulfate and chloride,224 and mercuric acetate,223 have been used, as well as halogens225 and nitro-sulfonates.226 The osazone acetates are converted into osotriazoles by nitrous acid,227 which decomposes the unacetylated osazones to the aldosuloses228 and the osazone formazans are cyclized with warm... 

Under the same conditions the 6,7-dodecanedione bishydrazone is converted to 36% 6-dodecyne and 19% 6-dodecene (35% Z, 65% E) . Remarkably no hexanonitrile is found in this case. In the oxidation of 1,2-bishydrazones to alkynes so far the chemical oxidants copper(II)salts mercuric oxide or nickel peroxide are superior to the nickel hydroxide electrode. 

Oxidation of 1,2-bishydrazones (494) is now known to give triazoles (495) and not dihydro-1,2,3,4-tetrazines. Possibly the latter are intermediates but are aromatized by ring contraction. 

Figure 9-24. The oxidation of the nickel(ii) complex formed from the template condensation of biacetyl bishydrazone with formaldehyde gives a neutral, conjugated complex, in which the ligand is doubly deprotonated.

In some cases a whole series of dehydrogenation reactions may proceed sequentially to yield aromatic or highly conjugated products. An example of this is seen in the aerial oxidation of the nickel(n) complex of the macrocycle formed by the template condensation of biacetyl bishydrazone with formaldehyde. The product of the oxidation is the fully aromatic dianionic macrocyclic complex (Fig. 9-24). 

Pure (6) can be prepared via the oxidative decomposition of the bishydrazone (7) with mercuric oxide 6) or thermal decomposition of the selenadiazole (8)7). 

If a very reactive cycloalkyne is synthesized, the necessary fast reaction at low temperature, must be worked up in a short period. These conditions are met by the oxidative decomposition of bishydrazones with lead tetraacetate in dichloro-methane. By this method the most strained, but still isolable cycloalkyne 3,3,7,7-tetramethylcycloheptyne (10) was prepared8), which on standing at room temperature... 

The reaction of 1,2-dibromocycloalkenes (13) with magnesium in the presence of l,3-diphenylbenzo[c]furan (16) affords a cycloalkyne adduct (17). Also, the mercuric oxide oxidation of bishydrazone, which has been used extensively in the preparation of open-chain and medium or large cyclic acetylenes " , is adapted for small ring bishydrazones (18) . Treatment of 18 with mercuric oxide in the presence of 16 or of phenyl azide results in the adducts, 17 and 19, respectively. It seems... 

Table 1. Yields of cycloalkyne adducts. I Grignard reaction II oxidation of bishydrazone III base elimination of bromomethylene derivative IV oxidation of aminotriazole V photolysis of tosylaminotriazole anion...

Krebs and coworkers have synthesized 3,3,6,6-tetramcthyl-l-thiacycloheptyne (55) . The thiacycloheptanedione (53) derived from the corresponding acyloin was converted into the bishydrazone (54). Oxidation of 54 with mercury(ii) oxide gave 55 in 5-5% yield together with the ew-olefin (56, 6-9%). In the absence of oxygen... 

The synthesis of 3,3,7,7-tetramethylcycloheptyne (64), a carbocyclic analogue of 55, has also been performed. The bishydrazone (63) derived from tetramethyl-cycloheptane-l,2-dione (62) was oxidized with lead tetraacetate and 64 was obtained together with 65, 66, 67 and 68. The last compound (68) is a dimer of 64 with... 

Cyclooctyne (75) can be prepared according to the usual rhethods of synthesis of acetylenic compounds. For instance, oxidation of the bishydrazone of cyclooctane-1,2-dione (74) " " or debromination of 1,2-dibromocyclooctene (76) with magnesium or the photolysis of the anion of I-tosyIamino-1,2,3-triazole derivative (77) gave cyclooctyne (75). 

Macrocyclic acetylenes containing one acetylenic linkage have been prepared by the oxidation of bishydrazones of macrocyclic 1,2-diones - >. This method has been used for the synthesis of 1,7-cyclododecadiyne starting from cyclododecyn-1,2-dione . 

Diketones have also been converted into alkynes, most commonly through the bishydrazone derivatives. Originally, cyclodeca-l,2-dione was converted into cyclodecyne by initial bishydrazone formation and subsequent oxidation with mercury(II) oxide (Scheme 76). More recently, cyclic... 

Oxidation of cyclooctane-1,2-dione bishydrazone (1) with mercuric oxide yields mainly (2) along with a little cyclooctyne, triazoles, and their mercury derivatives.4... 

Nitrogen compounds. Active Mn02 in ether proved useful for oxidation of the bishydrazone (1) to the purple bisdiazo compound (2), for yellow mercuric oxide, the usual reagent for an oxidation of this type, gave low yields. Pratt and McGovern ... 

Diphenylacetyiene, CeHsC CCsHs. Mol. wt. 178.22, m.p. 61°. Suppliers Farchan, Orgmet, A, B. Preparation from benzil by conversion into the bishydrazone and oxidation with yellow mercuric oxide in benzene (67-73% from benzil). ... 

Trapping of cycloalkynes and of bernyne. Wittig " demonstrated the transient formation of the C5-C7 cycloalkynes by oxidation of the appropriate 1,2-dione bishydrazones in the presence of either of two highly reactive Diels-Alder components, phenyl azide and 1,3-diphenylisobenzofurane. Thus oxidation of the C,-bishydrazone with mercuric oxide in refluxing benzene in the presence of powdered potassium hydroxide and 1 equivalent of the azide afforded the crystalline adduct in 29% yield. The cyclohexyne adduct was obtained in yield of 8%. 

Bishydrazones 126 and 127, unsubstituted at the nitrogen atoms, on oxidation immediately form 1-amino-1,2,3-triazoles in 20-60% yields [Eqs. (34) and (35)] (61CB3260 71JPR882). For 127, the reaction is sensitive to steric hindrance, and the formation only of l-amino-4-aryltriazoles is the evidence for this. 

Benzoin, tetraphenylethanediol, hydrazobenzene and 1,2-diphenyl-1,2-ethanedione bishydrazone are oxidized by methyl bis(l-naphthyl)bismuthi-nate to benzil, benzophenone, azobenzene and diphenylacetylene, respectively [88CL2021] (Section 5.2.4). Amides, thioamides, ureas and thioureas are A-acylated in good yield with acetic acid in the presence of the bismuthi-nate at room temperature [90CL1651] (Scheme 3.11). 

Tetramethyl-l-thiacycloheptyne (2).1 Cycloheptyne itself has never been prepared, but this seven-membered ring thiaalkyne, has been obtained in low yield by oxidation of the bishydrazone (1) with silver oxide in THF. It is... 

The oxidation of the bishydrazones of 1,2-dicarbonyl compounds yields 1-amino-1,2,3-triazoles... 

A great deal of effort bas been expended by Hauptmann s laboratory in the study of the oxidation of a,/3-bishydrazones (6.1-3) with metal oxides, but the yields are only fair (Eq. 9). " Comparable results have been obtained by El Khadem and his collaborators in the similar oxidation of osazone arylhydrazones. Recently, Alexandrou has reported the important observation that bissemicarbazones react well with lead tetraacetate to produce ureido-l,2,3-triazoles (6.1-4), which can be hydrolyzed to the corresponding amines (Eq. 10). Although the yields are still not very high, the method should receive further attention. 

Bis(onio)-substituted aryliodine(III) salts of type 453 are powerful oxidants. According to polarographic measurements, the Ei value for the acceptance of the first electron by bis(pyridinium) salt 453 is 1.3 V greater than for PhI(OAc)2, which is indicative of a dramatically increased oxidation power of 453 [570]. In particular, bis(pyridinium) salt 453 can instantaneously oxidize 1,2-bishydrazones to alkynes [570] and it reacts with diazoacetate esters at room temperature to give the corresponding a-aryliodonio diazo compounds [622],... 

Some earher methods start from 1,2-dicarbonyl systems. Bishydrazones 34 (R = H) of 1,2-dicarbonyl compounds are transformed into l-amino-1,2,3-triazoles 33 by oxidative cycbzation, for example, with Mn02 ... 

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