Diazenium

N-Hydroxy-N-nitrosamines with an aliphatic group at O2 produce a compound stable to aqueous acid and base (Fig. 3.4, 29) [158], whereas all other N-hydroxy-N-nitrosamines are susceptible to hydrolysis and appropriate 02-derivatives also render these materials vulnerable. The hydrolysis endpoint is the formation of nitroxyl (HNO) [which dimerizes to form nitrous oxide (N20)] and a C-nitroso compound. These products are formed from aryl [159] and alkyl bound unsubstituted diazenium-diolates as well as Oralkylated derivatives [160]. Studies of the solvolysis of Oi-alkyl derivatives are complicated by their tendency to decompose via competing radical pathways [161], but the Oi-benzyl derivatives are unique in that they hydrolyze back to the original synthetic precursors (Scheme 3.14) [162]. 

C>2-Tosyl diazeniumdiolates are quite stable and are the most studied derivatives [164]. Solvolysis in sodium methoxide solution generates the alkylated C-diazenium-diolate (Scheme 3.16), while under more neutral conditions a reaction analogous to that of the acyl compounds occurs. The added stability of the tosylates has enabled labeling studies, which have shown that these reactions are probably initiated by migration of the acyl and tosyl groups to Oi. 

Anodically electrogenerated species can undergo cycloaddition reactions with other reagents. For example, in Scheme 5 a diazenium cation reacts with styrene [8, 9]. 

The electrochemical oxidation of Af,Af-diarylhydrazines affords diazenium cations that undergo cycloadditions with olefins vide supra Scheme 5) [8, 9, 68-70]. Acetonitrile can participate in the formation of cycloadducts. 

In the medium pH range where both the diazenium cation and the diazene exist in solution, these two species react rapidly to afford a substituted tetrazene [141], The second oxidation wave, observed for disubstituted hydrazenes in acetonitrile with a pyridine base present, is due to the further oxidation of the tetrazene to a dicationic species. 

Dialkyldiazenes are unstable and lose nitrogen with the formation of two alkyl radicals. This is the only process observed when the 1,1-dialkyIhydrazine is oxidised in alkaline solution where none of the diazenium ion survives [144]. Electrochemical oxidation of the cyclic dialkylhydrazine 32 in an unbuffered solution... 

Aryl-4,6-bis(alkylthio)-l,3,5-oxa(thia)diazenium salts (231) are converted to 1,2,4-dithiazolines (233) by H2S presumably through ring opening under nucleophilic attack of H2S on C-2 and oxidation of the dithiol intermediate (232) by atmospheric oxygen (Scheme 48) <85LA1874,88LA729). 

H5C6-N = N-C6H5 H3C0-S02-R H3C N=N-CeH5 HsCs 1,2-Diphenyl-1 -m diazenium-sulfi R-SOje ethyl- mat 4... 

Oxygen substituted nitrenes have received much less study than aminonitrenes, but there have been some noteworthy recent developments. Toscano and co-workers " studied the photochemistry of diazenium diolates. The quantum yield of photodegradation was 0.10. 

Using orbital interaction theory wherever appropriate, discuss the chemistry of the diazenium dication of 2,7-diazatetracyclo[6.2.2.23 602,7]tetradecane 12+ (see Nelsen,... 

Nucleosides based on [l,2,4]triazolo[l,5-a]pyridine can be prepared by reaction between 3-nitro-2-pyridylhydrazine and the thioformimidate 48 followed by ammonolysis.62,63 A tetrahydrotriazolopyridinium salt (49) results from a reaction between a diazenium salt and an anil.64... 

Diazenium dications may also be considered gitonic superelectrophiles, but only a limited number of them have been prepared and studied.97 In principle, diazenium dications could be prepared by double alkylation or protonation of various azo-compounds. To date, only monalkylation has been achieved with strong alkylating agents (eq 57)97a However, Olah et al. showed that diazenium dications can be produced by double protonation of azobenzenes in FSQ3H-SbF5 at low temperature.97b It has also been demonstrated that the diazenium dications are prepared from electrochemical and chemical oxidations (eqs 58-59).97c,d... 

In the oxidation of 202, the tetracyclodiazenium ion 203 is produced in 81% yield. Like the hydrazinium dications, the diazenium dications exhibit relatively high acidities of their a-hydrogen atoms. 

The direct reaction of the polyamine with two equivalents of NO under appropriate conditions results in the formation of a stable zwitterionic diazenium-diolate moiety. Upon exposure to aqueous conditions, the diazeniumdiolate spontaneously decomposes into the polyamine precursor and two equivalents of NO. The kinetics of NO release are easily controlled by varying the structure of the amine precursor and/or environment (e.g., pH, temperature, solvent, etc.) In hydrophobic polymers, the NO release is slowed down as diazeniumdiolate decomposition is dependent on water uptake. 

Diazenium l,l-Dimethyl-2-[2-(l-methyl-2-pyrryl)-ethenylj- -pikrat E15/1, 1086 (R2N-N = CH-CHO + POCl3(COCl2)/ArH]... 

Scheme 30. Saturated-bridged bis(diazenium) and bis(hydrazine) intervalence compounds.

Alkyl-2-imidazolines 544 are in equilibrium with the enediamine tautomers 545 through which carbon-bound diazenium diolates 546 are formed upon reaction with nitric oxide (Scheme 125) <2005JOC7647>. 

Oxidation of a 1,1-disubstituted hydrazine in MeCN containing HCIO4 [132-134] or anhydrous HBF4 [135] forms a diazenium cation that may react with alkenes in a cycloaddition reaction to a tetrahydrocinnoline. If both substituents on nitrogen are aryl, an oxidative coupling between them may compete with the dipolar reaction [135]. 

The electrolysis of A/ -methylamides (LXX) results in the formation of iminium intermediates that undergo a [4 + 2]-cycloaddition with olefins [Eq. (26)] [252] to afford heterocycles (LXXI) in 45-58% yield. 1,1-Diphenylhydrazine can be dehydrogenated to the diazenium ion (LXXII) [Eq. (27)], which undergoes cycloadditions with olefins [253]. 

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