To form nitrenes

At high temperatures and low pressures, HN3 decomposes to form nitrene. 

Azides can be photoactivated to form nitrenes. Kitagawa and coworkers used 5-azido-l,3-benzenedicarboxylate (wbdc-N3) to form [Zu2(mbdc-N3)2(bpy)2l (CID-N3) and then irradiated this with ultraviolet radiation to convert the azide groups into nitrenes. The nitrene groups react with oxygen to give nitro- and nitroso- functionalities and with CO to give isocyanates. ... 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

Fig. 5. Chemistry of cyclized mbbei—bis-a2ide negative acting resist, (a) Preparation of cyclized mbber resin from polyisoprene (b) photochemistry of aromatic bis-a2ide sensiti2ers. The primary photoproduct is a highly reactive nitrene which may combine with molecular oxygen to form oxygenated products, or may react with the resin matrix by addition or insertion to form polymer—polymer linkages.

Sulfonic acid hydrazides, RSO2NHNH2, are prepared by the reaction of hydraziae and sulfonyl haUdes, generally the chloride RSO2CI. Some of these have commercial appHcations as blowiag agents. As is typical of hydrazides generally, these compounds react with nitrous acid to form azides (26), which decompose thermally to the very reactive, electron-deficient nitrenes (27). The chemistry of sulfonic acid hydrazides and their azides has been reviewed (87). 

The procedure described is essentially that of Shioiri and Yamada. Diphenyl phosphorazidate is a useful and versatile reagent in organic synthesis. It has been used for racemlzatlon-free peptide syntheses, thiol ester synthesis, a modified Curtius reaction, an esterification of a-substituted carboxylic acld, formation of diketoplperazines, alkyl azide synthesis, phosphorylation of alcohols and amines,and polymerization of amino acids and peptides. - Furthermore, diphenyl phosphorazidate acts as a nitrene source and as a 1,3-dipole.An example in the ring contraction of cyclic ketones to form cycloalkanecarboxylic acids is presented in the next procedure, this volume. 

The two principal means of generating nitrenes are analogous to those used to form carbenes. 

In contrast to diazido compounds [102] and [104], which throw off two azido groups and form silylene and germylene, photodecomposition of silyl azide [105] led to the generation of aminosilylene [107] via isomerization of initially formed nitrene [106] (Maier et al., 1989b). The IR spectrum of the... 

Note that the nitrene now allows a common intermediate that can be hydrogenated to anihne from both nitrobenzene and nitrosobenzene. It is also interesting to speculate on another route to form a nitrene on the surface. Phenyl hydroxylamine is a known intermediate whose concentration in solution is highly dependent upon reaction condihons. On adsorption of phenyl hydroxylamine one can write the following ... 

Internal nitrenes normally react at the adjacent position. Reduction of 2-(2-nitrophenyl)furan by ethyl phosphite yields furoindole derivatives in fair yield (34%) only, whereas much better results attend the pyrolysis of 2-(2-azidophenyl)furan.280 Furopyrazoles are obtained similarly.281 Azidofurans yield nitrenes that insert into adjacent CH links to form furo-pyrroles.282 Quite different results attend either the pyrolysis or the photolysis of azide 107a for the expected insertion into the side chain occurs giving the related indole but it is accompanied by the surprising replacement of furan oxygen by nitrogen producing 107b and similar products.283... 

Several reviews on the synthesis of aziridines have been published in the previous year. These publications include a review on the silver catalyzed addition of nitrenes (among other intermediates such as carbene) across a double bond <06EJOC4313> a review on sulfur ylide addition to imines to form aziridines <06SL181> a review on nitrogen addition across double bonds <06ACR194> a general review on functionalization of a,p-unsaturated esters with some discussion of aziridination <06TA1465>... 

Figure 4.21 BASED can react with molecules after photoactivation to form crosslinks with nucleophilic groups, primarily amines. Exposure of its phenyl azide groups to UV light causes nitrene formation and ring expansion to the dehydroazepine intermediate. This group is highly reactive with amines. The cross-bridge of BASED is cleavable using a disulfide reducing agent.

Figure 5.35 ABH reacts with aldehyde-containing compounds through its hydrazide end to form hydrazone linkages. Glycoconjugates may be labeled by this reaction after oxidation with sodium periodate to form aldehyde groups. Subsequent photoactivation with UV light causes transformation of the phenyl azide to a nitrene. The nitrene undergoes rapid ring expansion to a dehydroazepine that can couple to nucleophiles, such as amines.

The aziridines are the nitrogen analogs of the epoxides and undergo similar electrophilic reactions. No biological data were obtained for these compounds nor were they used as precursors to any CA-4, 7, analogs. They have been included since the synthesis is noteworthy, and they could be interesting intermediates. Xu et al. stereoselectively aziridinated chalcones using the nitrene precursor (PhINTS) and a copper catalyst to form compound 141 (Scheme 36) [82],... 

Aryl sulfinyl azides, ArS(0)N3, can be prepared at low temperature by reaction of sulfinyl chloride ArS(0)Cl with sodium azide (Maricich and Hoffman, 1974). On warming to 0° they decompose with evolution of nitrogen, their decomposition exhibiting clean first-order kinetics ( = 3 x 10-4 s-1 for PhS(0)N3 in acetonitrile at 0°). The rate-determining step of the decomposition is loss of nitrogen from the sulfinyl azide to form the sulfinyl nitrene ArS(0)N (143). The subsequent behavior of this nitrene suggests (Maricich and... 

FIGURE 7.10 Formation of the succinimido ester of IV-succinimidoxycarbonyl-P-alanine by reaction of three molecules of IV-hydroxysuccinimide (HONSu) with one molecule of dicy-clohexylcarbodiimide.25 The first molecule (N1) reacts to form the O-succinimido-isourea. The second molecule (N2) ruptures the ring by attack at the carbonyl, generating a nitrene that rearranges to the esterified carboxyalkyl isocyanate. The third molecule (N3) attacks the carbonyl of the latter. R3 = R4 = cyclohexyl SuN- = succinimido. 

This property is relatively rare in the very large number of reactions for which substituent effects were evaluated quantitatively106. It seems to be common, however, for all dediazoniations of arenediazonium ions and of related compounds, e.g. of substituted phenyl azides forming nitrenes, as well as for additions of carbenes to alkenes. 

Organoboranes react with ethyl 4-nitrobenzenesulphonyloxycarbamate under basic two-phase conditions in the presence of benzyltriethylammonium chloride or Aliquat to yield ethyl (V-alkylcarbamates [38]. The reaction probably proceeds via the initial formation of the nitrene, which reacts with the borane to form a B -N+ zwitterion. Subsequent rearrangement and solvolysis leads to the product. Aliquat is the better catalyst for the higher-molecular-weight boranes. 

FeCl2 has been used to catalyse nitrene transfer from l-butyloxycarbonyl azide to sulfoxides (to form sulfoximides), sulfides (to give sulfimides), and a ketene acetal (to form an a-amino ester). ... 

Figure 16. Crosslinking reactions in bisarylazide-rubber resists. The primary photoevent is production of a nitrene which then undergoes a variety of reactions that result in covalent, polymer-polymer linkages. A schematic representation of crosslinking via nitrene insertion to form aziridine linkages is shown together with several other reaction modes available to the...

However, in the ground state, the main contributions to the resonance hybrid are due to forms 3a,b. Their importance increases going from diazopyrroles to the diazotetrazole, so that the diazo structure with cumulated double bonds, which has been extensively employed as a shortened form for the diazoazoles, does not seem to depict them correctly any more. Therefore, in continuation of this review, the diazoazoles will be represented by structure 3a unless other limiting forms better account for the observed reactivity. In fact, even the nitrene-like form, a heteroanalogue of 17, which is the one with highest energy, has been invoked to explain the reactivity in some cycloaddition reactions (86CC1127). 

Flash vacuum thermolysis of 6-chloro-3-diazoindazole (2b) resulted, upon loss of nitrogen, in the formation of carbene 102, which could intra-molecularly rearrange to the nitrene 103, or to the azabenzocyclopropene 104, or to azacycloheptatrienylidene 105 (Scheme 29). The only isolable product was 106, formed by dimerization of the nitrene 103 (78CB2258). 

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