Phenyl azide, dipolar additions

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]. 

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 thermal cycloaddition of azides to acetylenes is the most versatile route to 1,2,3-triazoles, because of the wide range of substituents that can be incorporated into the acetylene and azide components. The accepted mechanism for the reaction is a concerted 1,3-dipolar cycloaddition. The rates of addition of phenyl azide to several acetylenes have been measured the rates of formation of the aromatic triazoles are not appreciably different from the rates of cycloaddition to the corresponding olefins, indicating that the transition-state energy is not lowered significantly by the incipient generation of an aromatic system. 

Cycloaddition of p-methoxyphenyl azide to alkynic dipolarophiles at room temperature gives triazoles (697) and (698) (Equation (54)). A regiospecific addition is only observed in the case of Z = CH(OMe)2 <89H(29)967>. Phenyl azide and substituted benzyl azides undergo 1,3-dipolar cycloadditions with DM AD, phenylacetylene, and ethyl propiolate to afford 1-phenyl- and 1-benzyl-... 

Compound 156 (prepared by reaction of tetrabromocyclopropene and 2,5-dimethylfuran) underwent dipolar cycloaddition with phenyl azide to produce the fused triazole 157. The reaction was carried out in dichloromethane at room temperature over 2 days. This lower reaction temperature allowed for the isolation of the adduct 157, which was established by X-ray crystallographic analysis to be the product of ct>-selective addition. Heating triazole 157 in benzene at reflux for 2 h resulted in ring expansion producing a 1 1 mixture of compounds 158 and 159 (Scheme 16) <2004JOC570>. 

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 ... 

The rates of 1,3-dipolar addition of mesitonitrile oxide to cis- (36a) and frans-cyclooctene (37a) and some other cyclic olefins have been discussed with respect to strain effects (271). It was concluded that frontier orbital energies of the alkenes and differences in olefinic strain energies do not correlate with the observed reactivities. The relative rates for addition of phenyl azide to several alkenes and the olefinic strain energies are shown in Table 31 (272). 

A final example is a 1,3 dipolar addition to pendant azide groups. The reaction takes place with phenyl vinyl sulfoxide in dimethylformamide. Forty-eight hours at 110 °C are required for the azide groups to become undetectable by infrared spectroscopy. The product precipitates out with addition of ether ... 

Nitrile oxides add in a 1,3-dipolar fashion to the double bond of cyclopropenes and diazomethane adds to give a pyrazoline (729) in good yield. Phenyl azide shows a very fast rate of reaction with 3,3-dimethylcyclopropene compared with additions to other olefins, evidently due to the influence of strain release in lowering the transition state of reaction, but the initial adduct is not stable and undergoes a reverse... 

The 1,3-dipolar addition of secondary diazo-compounds to 1,3,3-trimethylcyclo-propene affords 2,3-diazabicyclo[3,l,0]hex-3-enes [cf. (130)], but with diazoacetic ester this product, with an acidic proton at C-4, undergoes rearrangement to ethyl 3,4,4-trimethyl-l,4-dihydropyridazine-6-carboxylate. Further additions of phenyl azide to methylenecyclopropanes have shown that the presence of a carboxylate group in the three-membered ring causes the initially formed spirodihydrotriazole to undergo rearrangement to a 4-substituted 1,2,3-triazole. ... 

The relative reaction rates of the 1,3-dipolar cycloaddition reaction of phenyl azide to dipolarophiles containing the C=C bond can be predicted by using the Jaguar V. 3.0 ab initio electronic package. Thermodynamic analysis of the 1,3-dipolar cycloaddition of organic azides with conjugated nitroalkenes at 273-398 K shows that temperature does not affect the course of these reactions in the vapour phase. Density-functional procedures have been used to explain the regioselectivity displayed by the 1,3-dipolar cycloaddition of azides with substituted ethylenes. A density-functional theory study of the 1,3-dipolar cycloaddition of thionitroso compounds with fulminic acid and simple azides indicates that the additions are not stereospeciflc. ... 

A number of cyclopropyl-substituted five-membered heterocycles have been synthesized by addition of various 1,3-dipolar reagents to (alk-l-enyl)cyclopropanes. Most reactions were performed using tricyclo[3.1.0.0 ]hex-3-ene and tricyclo[3.1.0.0 ]hex-3-en-3-yl phenyl sul-fone, giving the corresponding cycloadducts in very good yields on treatment with azides, a carbonyldicobalt complex, nitrile oxides, diphenylni-trilimine, (4-nitrophenyl)benzenecarbonitrile ylide, and diazoalkanes. For example, addition of tricyclo[3.1.0.0 ]hex-3-ene (1) to 4-nitrophenyl azide gave dihydro-1,2,3-triazole 2 in 94 /o yield. ... 

In a related piece of work, imidazolines have been prepared from A -chloro-N-phenyl amidines and enamines. (Scheme 79). Pyrazomycins have been synthesized by the Roche group, the key step being the preparation of the pyrazolone ring by the addition of toluene- -sulphonyl azide to the anion from diethyl acetone dicarboxylate (Scheme 80). Imidazolidines (201) have been prepared by the action of isocyanates and isothiocyanates with an aziridine ester a dipolar intermediate is implicated. Imidazolidine-4,5-diones have been prepared by the... 

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