Reductive cleavage of hydrazines

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 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]. 

S LiAIH4 O-OTh.n W v-sN NHAc r [26] DIBAL has been used in the reductive cleavage of resin-bound esters to alcohols Alkenes and alkynes can both be reduced. Other reductions include nitrile to amine. diazo to hydrazine disulfide to thiol epoxide to alcohol [26, 63] [67.74] [123] [158] [180] [227] [251] [274-276]... 

Reductive N-N cleavage of hydrazines. A diastcreoselective synthesis of chiral a-amino aldehydes (4) from glyoxal involves an intermediate dimethylhydrazone (1), which reacts with an alkyllithium to provide an or-substituted N. N -dimcthylhydrazine (2). The mildest method for cleavage of hydrazines to primary amines (3) involves hydrogenolysis catalyzed by Raney nickel at 30-50. This Raney nickel reductive cleavage is markedly improved by sonication and proceeds at atmospheric pressure of H2 at 20 in CHjOH in yields of 66-84% with no raccmization or debenyzlation.1... 

Other reaction substrate variations that will not be covered in this chapter include the NaBHt/TFA reductive cleavage of 1,4-epoxy-1,4-dihydronaphthalenes25 and benzylic ozonides,26 the tandem solvolysis-reduction of triarylmethyl chlorides,27 the cleavage of ferrocenyl ketone hydrazines,28 and the reduction of benzophenones to diarylmethanols ( ).29... 

Mild reduction converts azines and hydrazines into disubstituted hydrazines, but under vigorous conditions reductive cleavage of the N-N bond affords amines. Reduction of oximes thus affords a further but seldom used method of converting carbonyl compounds into amines. 

Reductive cleavage of diaryl diselenides. - Generation of arylselenide anions by hydrazine hydrate i.s most convenient under basic conditions. 

---