Heteroaryl Azides

2 Heteroaryl Azides - 2-Pyridyl azides exist in equilibrium with bicyclic tetrazoles, with the latter predominating under normal conditions. A number of trifluoromethyl-substituted derivatives of tetrazoles, e.g. (53), have been synthe- 

Photochemical studies of azido-3-phenylcoumarins in solution and in polymer layers have been described. A derivative of NAD and the corresponding ATP analogue have been synthesized in which a spin label is attached to the N-6-position and an azido function to the C-2 atom of the adenine ring. Both compounds were shown to be active coenzymes or substrates for various enzymes, and could be covalently incorporated into the enzymes upon photolysis. 

Photoreactions of the analogous tetrazolo[l,5-a]pyrimidine with benzene and substituted benzenes in the presence of trifluoroacetic acid seem to involve the intermediacy of the 2-pyrimidylnitrenium ion.  

Laser photodissociation of ketene at 230 nm has been investigated in molecular beams. The experimental rovibrational population distribution has been compared to predictions from phase-space theory for the channels leading to CO + CH2(a Ai) and CO + CH2(b Bi). The calculations are not compatible with the latter channel, suggesting that it does not contribute significantly to the dissociation process. The photodissociation of singlet ketene by two-step IR + UV excitation has been studied using state-selective detection of CH2 by laser-induced fluorescence, and the results compared with 

Other studies of CO loss from small molecules include the photolysis of OCS on Ag clusters, in which an odd-even dependence on the number of Ag atoms in the cluster was discovered. OCS desorbs non-dissociatively from even numbered clusters, but dissociates to CO and AgnS on odd numbered clusters. This alternation correlates with the ionization potentials of the naked metal clusters, and the photoreactivity pattern can be explained in terms of a charge-transfer mechanism. A numerically efficient algorithm has been developed in the theory of ladder-climbing and IR multiphoton dissociation, and has been applied to HCO.  

10 K induces decarboxylation, and a complex between the carbene (47) and CO2 is formed. Further irradiation of this carbene at 254 nm does not produce detectable amounts of imidazole while irradiation at 193 or 185 nm results in decomposition to acetylene, acetonitrile, methyl isocyanide, the ylide H2C-NCH, and HCN. 

Oligonucleotides containing the photoreactive nucleosides, 2-azido-2 -deoxyi-nosine and 8-azido-2 -deoxyadenosine, have been prepared.  

The research on photoelimination of CO and CO2 covered by this review consists mainly of studies of photodecarbonylations of small molecules, such as ketene, or of metal carbonyls. 

1 Ptiotoeliiiiiiiation of CO and CO2 from Organometallic Compounds - There have been several reviews covering various aspects of the photodissociation of metal carbonyls. These include quantum chemistry and photodynamics, photo- 

The photolysis of bis-[chloro(dicarbonyl)rhodium] has also been investigated in frozen gas matrices at 12 K and Nujol mulls at 77 K, under which conditions facile loss of the terminal CO ligands occurs, while the [(Cl)Rh]2 bridging unit is retained. Photolysis of (58, M = Fe) in the presence of phosphines or phosphites results in the formation of simple monocarbonyl-substitution products, while acetylenes react photochemically with the diiron compound to give vinylketone-bridged derivatives (59, R=Ph,C02Me). In contrast, photolysis 

Photochemical reactions of Ru3(CO)i2 and Os3(CO)i2 with nitrogen hetero-cycles have been studied, with substitution products being formed in most cases. For example, with pyridine the ruthenium compound forms the ortho-metallated complex Ru3H(CO)i i(CsH4N), while the osmium compound gives the simple substitution product Os3(CO)n(py). The novel dihydrido triruthenium cluster H2Ru3(CO)io can be synthesized by photolysis of Ru3(CO)i2 under an atmosphere of dihydrogen. 

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Active methylene nitriles condense with o-substituted aryl and heteroaryl azides in a two-step process to give tricyclic triazolopyrimidines without isolation of the triazole intermediates <85BSB441, 87BSB587). 5-Azido-4-formyltriazoles (758) condense with dimethyl 3-oxopentanedioate and tri-ethylamine in ethanol to give 5-(triazol-l-yl)-4-formyltriazoles (759), which undergo cyclization to... 

Aryl and heteroaryl azides are known to undergo ring expansion to azepines on photoelimination of nitrogen in the presence of nucleophiles. Evidence for benzazirine and 1-azacycloheptatetraene intermediates has previously been described and both species continue to be invoked to explain transformations of this type. The presence and nature of substituents appears to influence the course of the reaction, with electron-withdrawing substituents promoting azepine formation. o-Substituted aryl azides (102) are converted on irradiation in methanol-tetrahydrofuran into the 3-substituted 2-methoxy-3H-azepines (103). A pathway via the benzazirine (104) is proposed in Scheme 4, although... 

The photoreactions of heteroaryl azides have also been examined in detail. Loss of nitrogen followed by ring expansion... 

Studies of the photoreactions of aryl and heteroaryl azides have also been described. Nitro-substituted aryl azides... 

Heteroaryl azides frequently undergo ring expansion on photoelimination of nitrogen fused azirine intermediates have been proposed. Irradiation of the 4-azidoisoquinolines (91), for... 

The chemistry of heteroaryl azides is complex and its careful consideration is beyond the scope of the present chapter. Smith s [21] 1984 review presents a thoughtful analysis of the then existing results for this class of compounds. Here we focus exclusively on the chemistry of 1,3,5-triazinyl azides because they illustrate an important issue in nitrene chemistry—the spin multiplicity of the ground state. 

Heteroaryl azides undergo analogous photochemically induced ring expansion reactions. The 3-methoxy-4-azidopyrid-azines (87) were converted in this way via the unstable lH-1,2,5-triazepines (88) into the 4H-1,2,5-triazepines (89) on irradiation... 

Compared with studies of aryl and heteroaryl azides, work on aliphatic azides remains uncommon. No doubt one reason for this is the generally lower stability of aliphatic azides. Perfluoro(2-methyl-2-pentene) reacts with sodium azide at... 

The photoehemistry of organic azides has been reviewed.In addition to the photolysis of alkyl, vinyl, acyl, aryl and heteroaryl azides, this review also... 

Suna and coworkers developed an elegant one-pot azidation of heterocycles by in situ formation of heteroaryl(phenyl)iodonium tosylates from heteroarenes, DIB, and tosic acid, with subsequent Cu-catalyzed azidation (Scheme 7) [115], The unstable heteroaryl azides were converted in situ to triazoles by click reactiOTi with alkynes, or reduced to the corresponding amines in high yields over the three-step/one-pot sequence. The heteroaryl moiety was chemoselectively transferred to the nucleophile, demonstrating the preference to transfer the more... 

Scheme 3.30 Solid-phase synthesis of heteroaryl azides via nucleophilic aromatic substitution" ...

Scheme 3.32 One-pot synthesis of i, 4-disubstituted i, 2,3-triazoles via cycloaddition of aryl and heteroaryl azides prepared in situ from the corresponding aryl halides ...

The in situ preparation of aryl and heteroaryl azides from the corresponding aryl halides via L-proline-promoted Cnl-catalyzed coupling reactions in the presence of alkynes allows the one-pot synthesis of 1,4-disubstituted 1,2,3-triazoles (e.g. 226). Liang et al. also reported the one-pot synthesis of 1,4-disubstituted 1,2,3-triazoles (e.g. 227) from aryl bromides or iodides and terminal alkynes in the presence of sodium azide using diamine-promoted Cnl-catalyzed reactions. It has also been shown that this type of synthesis can be carried out in a mixture of the ionic liquid [bmim][BF4] and water (Scheme 3.32). Starting with boronic acids, the catalytic approach to aryl azides and l-aryl-1,2,3-triazoles can be carried out under milder reaction conditions and improved substrate tolerance (Scheme 3.33). In fact, it was demonstrated that both electron-rich and electron-poor aryl boronic acids 228 could be efficiently converted into the corresponding aryl azides (229) in the presence of sodium azide and CUSO4. A one-pot protocol... 

Aryl azides and heteroaryl azides can be prepared by the reaction of aromatic amines with trifly 1 azide. This straightforward approach to aromatic azides can be carried out under mild reaction conditions. In fact, the reaction of 8-aminoquinoline (262) in dichlorometh-ane/methanol occurs at room temperature in the presence of triethylamine and copper sulfate to afford 8-azidoquinoline (263) in 95% isolated yield. The reaction of aryl amide salts 265, generated from the corresponding anilines 264 and strong bases, with tosyl azide also affords aryl azides 266 (Scheme 3.38). ... 

For the azidation of heteroaromatic substrates, in 2012, Suna s group reported a one-pot multistep protocol to prepare heteroaryl azides (Scheme 6.8) [49]. In their procedure, heteroaryl(phenyl)iodonium azides A are prepared in situ, which undergoes a copper(l)-catalyzed regioselective fragmentation to generate the... 

Schuster, G. B. and Platz, M., Photochemistry of phenyl azide, Adv. Phototochem., 17, 69,1992. Smith, P. A. S., Aryl and heteroaryl azides and nitrenes, in Azides and Nitrenes, Reactivity and Utility, Scriven, E. E, Ed., Academic Press, Orlando, FL, 1984. 

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