Azides, 1,3-dipolar addition

The interaction of diazomethane with 1-azirines was the first example of a 1,3-dipolar cycloaddition with this ring system (64JOC3049, 68JOC4316). 1,3-Dipolar addition produces the triazoline adduct (87). This material can exist in equilibrium with its valence tautomer (88), and allylic azides (89) and (90) can be produced from these triazolines by ring cleavage. 

The reactions of enamines as 1,3-dipolarophiles provide the most extensive examples of applications to heterocyclic syntheses. Thus the addition of aryl azides to a large number of cyclic (596-598) and acyclic (599-602) enamines has led to aminotriazolines which could be converted to triazoles with acid. Particular attention has been given to the direction of azide addition (601,603). While the observed products suggest a transition state in which the development of charges gives greater directional control than steric factors, kinetic data and solvent effects (604-606) speak against zwitterionic intermediates and support the usual 1,3-dipolar addition mechanism. 

Extensions of 1,3-dipolar additions of aromatic azides (720,721) to other enamines (636), and particularly to the enamine tautomer of SchilTs bases, were explored (722,723). Further nitrone additions were reported (724,725) and a double nitrile oxide added to an endiamine (647). Cyanogen azide and enamines gave cyanoamidines through rearrangement (726). 

Friesner and coworkers investigated the 1,3-dipolar addition of phenyl azide 60 to carbon-carbon double bonds forming l-phenyl-4,5-dihydro-l//-l,2,3-triazoles (61 and 62) (Scheme 39) [99JPC(A)1276]. 

Because of resonance stabilization of the anion, a tet-nazolyl moiety is often employed successfully as a bioisosteric replacement for a carboxy group. An example in this subclass is provided by azosemide (27). Benzonitrile analogue is prepared by phosphorus oxychloride dehydration of the corresponding benzamide. Next, a nucleophilic aromatic displacement reaction of the fluorine atom leads to The synthesis concludes with the 1,3-dipolar addition of azide to the nitrile liinction to produce the diuretic azosemi de (27). ... 

Carbon-carbon triple bonds can also undergo 1,3-dipolar addition." For example, azides give triazoles ... 

Dipolar addition to alkenes also occurs with species other than ozone, often to give products much more stable than the labile molozonides (54), e.g. addition of azides (61) to give dihydrotriazoles (62) ... 

Buchanan and coworkers71 prepared the /3-D-ribofuranosyltriazole 287 by dipolar addition of benzyl azide to the /3-d-ribofuranosylethyne 70. Related analogs have been reported by others.113a,205a,205b The anomeric 3-phenyl-4-D-ribofuranosylpyrazoles have been prepared by a dipolar, addition reaction.2050... 

The aroyl-substituted heterocyclic ketene aminals 482 react with 4-chlorophenyl azide to give polysubstituted 1,2,3-triazoles 483 and imidazo[ 1. Z-r 1.2,4]triazoles 39 (Equation 112) <2000HAC387>. Polysubstituted 1,2,4-triazoles are formed by the nucleophilic attack of the ct-carbon of the azide. Then, through the cyclocondensation and aromatization sequences, the fused heterocycles resulted by a 1,3-dipolar addition at first, and then through a Dimroth rearrangement and deamination of chloroaniline <1992JOC184>. 

From Azides and x-Acylphosphorus ylids Addition of azides to a-acylphosphorus ylids takes place at room temperature in dichloromethane or at 80°C in benzene, giving triazolines from which a phosphine oxide is spontaneously eliminated. " The ylids exist almost exclusively in the cis-enolate configuration, and a mechanism involving concerted 1,3-dipolar addition has been proposed (Scheme 12) on the basis that there is a low entropy of activation for the reaction, and that the reaction rate is insensitive to changes in solvent polarity. ... 

Aziridines can be prepared directly from double-bond compounds by photolysis or thermolysis of a mixture of the substrate and an azide.812 The reaction has been carried out with R = aryl, cyano, EtOOC, and RS02, as well as other groups. The reaction can take place by at least two pathways. In one, the azide is converted to a nitrene, which adds to the double bond in a manner analogous to that of carbene addition (5-50). In the other pathway a 1,3 dipolar addition (5-46) takes place to give a triazoline (which can be isolated), followed by extrusion of nitrogen (7-46). Evidence for the nitrene pathway is most compelling for... 

The addition reactions of organic azides to unsaturated systems can occur by two mechanisms.1 If the reaction temperature is lower than the decomposition temperature of the azide, a 1,3-dipolar addition is observed. When, however, the reaction is carried out at the wavelength or at the decomposition temperature of the azide, the addition proceeds through an intermediate nitrene. 

Huisgen has stated that the driving force behind the 1,3-dipolar addition is stronger the more the loss of T-bond energy in the reactants is overcompensated by the energy of the two new bond energy is O-N < N-N < C-N, azides do not add at all to aldehydes and ketones and add with more difficulty to nitriles than to olefins. Phenyl azide, for instance, adds preferentially to the C-C double bond of acrylonitrile.194 103 This is also the reason why the condensation products of aldehydes and primary amines, which essentially exist in the Schiff-base structure 46a, react in the tautomeric enamine form 46b.2 ... 

One-pot synthesis of aziridinyl ketones including the initial dipolar addition of azides to the ethylene bond with subsequent elimination of the nitrogen by photolysis is also possible [55, 56]. For example, in the case of azidocarboxylic acid ethyl ester 35,2-oxo-7-azabicyclo[4.1.0]heptane-7-carboxylic acid ethyl ester 37 was synthesized via the formation of the cycloadduct 36 [55] (Scheme 1.10). 

The nitrene precursor (usually the azide) undergoes 1.3-dipolar addition to give triazoline, which can loose nitrogen, but does not involve a free nitrene. 

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