Nitrenes azides reaction

The main example of a category I indole synthesis is the Hemetsberger procedure for preparation of indole-2-carboxylate esters from ot-azidocinna-mates[l]. The procedure involves condensation of an aromatic aldehyde with an azidoacetate ester, followed by thermolysis of the resulting a-azidocinna-mate. The conditions used for the base-catalysed condensation are critical since the azidoacetate enolate can decompose by elimination of nitrogen. Conditions developed by Moody usually give good yields[2]. This involves slow addition of the aldehyde and 3-5 equiv. of the azide to a cold solution of sodium ethoxide. While the thermolysis might be viewed as a nitrene insertion reaction, it has been demonstrated that azirine intermediates can be isolated at intermediate temperatures[3]. 

Reaction of metal nitrosyls with azide ion proceeds with formation of N2 and N20 (56). This can be viewed as the result of a nitrene transfer reaction in analogy with the Curtius rearrangement (62) and its organome-tallic counterpart (63). 

The results have been corroborated by further studies of o-(allyloxy)phenyl azide and 14 derivatives substituted on the allyl group. The allyloxy azide in Scheme 39 underwent complete conversion to triazoline at 35°C in 3 weeks as indicated by NMR.197 Thermolysis of o-allylphenyl azides, on the other hand, required high temperatures of the order of 155-200°C, apparently suggesting nitrene insertion reactions.197 The higher rate of decomposition of ortho-substituted phenyl azides as compared to the corresponding meta or para isomers, noted primarily in those systems where the ortho substituents have... 

Triazines have been formed from the reaction of imidazol-2-ylidenes with azides.68 The reaction could be thought of as the reaction of a carbene with a nitrene. The reaction gives 54-94% yields and one of the products was induced to lose nitrogen when heated to above 120 °C. 

With respect to the electronic structure, nitrenes are analogous (isoelectronic) to carbenes. As in the case of diazocompounds, photolysis as well as thermolysis of azides leads to the corresponding nitrenes. Some reactions are collected in the following scheme ... 

The azabicyclononane system is a common structural feature in diterpene alkaloids, and the nitrene insertion route to the ring system has been studied in detail in model decalins as well as in steroids (Scheme 11). Thus irradiation of the rrans-acyl azide (21) gave, in addition to isocyanate (30-33%), a mixture of Ae 7- and 8-lactams (22) and (23). The y-lactam (22) predominated, dthough the overall yield was poor. > The corresponding c/s-azide (24), however, gave the 8-lactam (25) as Ae major product, again in low yield. One elegant application of this type of intramolecular nitrene insertion reaction... 

The intramolecular aziridination of 2-(alkenyl)phenyl azides was best performed under pho-tolytic conditions116-117, generating the nitrene (ca. 0.001 M solution in cyclohexane, 350 nra, Rayonet Photoreactor)118. The nitrene addition reaction proceeded with complete diastereose-lectivity, the double bond geometry was retained in the aziridine thus produced. The alkaloid ( )-virantmycin was synthesized from the aziridine 2117. 

Another related zirconium complex 32 containing redox active tridentate NNN pincer ligand catalyzes nitrene transfer reactions from organic azides to f rf-butyl isocyanide to form non-symmetrical carbodiimides where the metal maintains the Zr(IV)... 

Nitrene insertion. A nitrene insertion reaction is central to many syntheses of pyridoacridine alkaloids and their analogues. For example, Labarca et al. [87JCS(P1)927] have reported a three-step synthesis of a pyridoacridine 169 starting from 2-methoxyacridine-9-carboxaldehyde 165 (Scheme 26). Cyclization of the vinyl azide 166 by thermolysis is believed to involve a nitrene insertion reaction, to give either 167 or 168. 

K. In addition, it was found that the irradiation of 22 in benzene in the presence of both cis- and rans-pentenes (0.05 to 3 M) produces a mixtiu-e of aziridines, which is typical of the presence of both singlet and triplet nitrene cycloaddition reactions. The triplet-triplet absorption spectrum of azide 22 was detected, and it was found that naphthalene inhibits the photoreaction of 22 by quenching of its triplet state. It was concluded, therefore, that the ground state of nitrene 23 is a triplet and that it is formed exclusively upon sensitized photolysis of azide 22 through the triplet state of 22. 21 Nq isocyanate was detected in the photolysis products of 22. 

Azide anion is a good nucleophile. Many azide reactions proceed via formation of an active intermediate, nitrene, analogous to carbene. This results from the photolysis of hydrazoic acid ... 

Azido compounds are versatile molecules. They are used extensively in both organic reactions and chemical biology. All azides are potentially explosive and must be handled with care. Azides, which have been known for over 100 years, are the most widely used precursors of nitrenes. like diazo compounds, they possess a linear 1,3-dipolar stracture and are easily prepared, often by introduction of the azide (Nj ) ion from inorganic salts such as sodium azide. The thermal stability of azides is critically dependent on the substituent on nitrogen. Most azides decompose thermally in the range 100-200 °C to give nitrenes. Azides are also readily decomposed photochemically, and this is often the method of choice, particularly for mechanistic studies. Like diazo compounds, the decomposition of... 

Copper-catalyzed decomposition of benzenesulfonyl azide in the presence of cyclohexene was the first reported evidence of a metal-catalyzed nitrene insertion reaction [25]. This seminal discovery was then followed by the pioneering work of Breslow and Gellman who introduced the use of iminoiodinanes as metal nitrene precursors as well as rhodium dimer complexes as catalysts [26,27]. They showed the formation of the corresponding benzosultam in 86% yield in the presence of rhodium (II) acetate dimer (Rh2(OAc)4) via an intramolecular metal nitrene C—H bond insertion reaction (Eq. (5.1)). 

Nitrene addition reactions have somewhat more scope when the reactions are carried out by azide photolysis for example, the acyinitrene pivaloylnitrene adds in moderate yield and with good stereoselectivity to cj>alkenes when it is generated from pivaloyl azide by photolysis in dichloromethane." Similarly p-cyanobenzoylnitrene, when generated by photolysis of the azide 21 in the presence of 2,5-dihydrofuian, gives the aziridine 22 in moderate yield (Scheme 6.11)." This nitrene and other p-substituted benzoylnitrenes also react with Cgo to give fulleroaziridines such as 23." ... 

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