Hydrazines reductive cleavage

The alkoxycarbonyl group activates the N — N bond, so that a racemization-free reductive cleavage by treatment with a large excess of lithium in liquid ammonia is possible (sec procedure below). This method is not suitable for hydrazines containing a benzylic C-N bond, because it is cleaved under the reducing conditions. 

Reductive cleavage of the N-N bond in bicyclic systems containing a ring junction hydrazine subunit presents a facile route to medium-sized heterocycles containing two or more nitrogen atoms and the subject was duly covered in CHEC-II(1996) <1996CHEC-II(8)747>. No substantial progress has been reported since its publication. 

SL901>. Reductive cleavage of 5-silyl, 3-, 4- and 5-silylmethylisoxazoles gave their corresponding silyl P-enaminones, which on reaction with hydrazines, provided regioselective syntheses of 3- or 5-silylpyrazoles and 3-, 4- or 5-silylmethylpyrazoles, respectively <06T611>. 

Arylazo tosylates of type 248, which are readily obtained from aniline derivatives 249 in a two-step procedure (equation 162), can be alternatively used as starting materials. This electrophilic nitrogen equivalent 248 reacts with a broad range of functionalized Grignard reagents under mild conditions. Subsequent allylation of the addition products with allyl iodide, followed by reductive cleavage of the resulting hydrazine derivatives... 

The N-N bond of polystyrene-bound hydrazines, which are prepared by reaction of organolithium compounds with resin-bound hydrazones [457], can be cleaved by treatment with borane to yield a-branched, primary amines (Entry 9, Table 3.23). An additional example of reductive cleavage to yield amines is shown in Entry 10 (Table 3.23), in which a resin-bound a,a-disubstituted nitroacetic ester undergoes decarboxylation and reduction to the primary amine upon treatment with lithium aluminum hydride. 

The twelve-membered cyclo-dipeptide glidobamine will be synthesized using the reductive cleavage of the nitrogen, nitrogen bond in a hydrazine derivative as a key step [76]. 

The hetero Diels-Alder reaction of y-dienyl N-acylazo compounds, formed by oxidation of the hydrazine derivative 25, yields bicyclic diazepines 26 in excellent yields. The reductive cleavage of the N-N bond yielded 6-substituted caprolactams 27 <07JOC6816>. 

Reaction of aryl azides with hydrazine hydrate can result in reductive cleavage of the azido group. Azidobenzene gives a mixture of benzene and aniline when heated with an excess of hydrazine hydrate in ethanol. If there is an acyl or an alkoxycarbonyl group at the ortho position, cyclization products are formed instead for example, methyl 2-azidobenzoate gave indazolinone (13 90%). 

A-nitroso and A-nitro compounds may both be reduced to hydrazines. In this case care must be taken to avoid a reductive cleavage of the nitrogen-nitrogen bond [79,81]. Several other reductions by Na(Hg) has been described by Funke in his review [79]. 

A reaction that involves both a carbon-carbon and a nitrogen-nitrogen cleavage is found in the reduction of 2-phenyl-4-carboxytriazole by Na(Hg) in slightly alkaline solution [118]. The reaction probably starts with a reductive cleavage of the ring, followed by loss of CN and further reduction of the phenylhydrazone thus obtained to the hydrazine ... 

Organometallic complexes of uranium(vi) with organoimido and oxo functional groups Cp 2U(=NR)(=E) (E = NR or O) have also been prepared by two-electron oxidative atom transfer using organic azides, amine A-oxides or nitrous oxide. Another way of generating the compounds is reductive cleavage of 1,2-disubstituted hydrazines (Scheme 54).119-121... 

A particularly interesting aspect of electrochemistry is that it may allow transformations of bound substrates, by coupling proton(s) and electron(s) transfers. This makes possible to mimic certain steps of the reactions driven by metalloen-zymes. For example, the nitrosyl ligand in 7 (Sch. 6) is activated toward protic attack. Controlled potential reduction of 6 at the potential of the second process in the presence of PhOH (5-10 equiv) as a proton source consumed 6 F mol 6 and afforded the molybdenum oxide MoO(l,2-Ci, 11452)2] 8 and ammonia. The reductive cleavage of the N—O bond was proposed to involve a hydroxylamide intermediate, Sch. 7 [27]. Relevant to this is the fact that the chemical reduction of [Mo(NO)2(dttd)] by sodium borohy-dride or hydrazine in methanol produced [Mo(NO)(NH2O)(dttd)] with a side-on hy-droxylaminyl ligand [28]. 

Chiral hydrazines, supported on Merri-field resin, were reacted with various aldehydes, affording the corresponding hydrazones. These compounds allowed stereoselective preparation of a-branched amines, through 1,2-addition of both aromatic and aliphatic nucleophiles to the C=N double bond of the hydrazones. Reductive cleavage released the desired amine from the resin. Moderate to good enantiomeric excesses (50-86%) were achieved. 

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