Alkene and azide

Minisci, Galli and co-workers have studied a variety of radical reactions which result in the formation of organic azides. These processes commonly involve the interaction of an organic peroxide, an alkene, and azide ion in the presence of a ferrous-ferric redox system. The initial step is the reduction of the peroxide by Fe " " to form a free alkoxy radical (Fenton reaction, equation 104). 

Some applications of the triazoline route to aziridines from alkenes and azides are described below. 

Thermolysis of 2-diazo-l,3-dithiane, prepared in situ from the reaction of 2-lithio-2-trimethylsilyl-l,3-dithiane and tosyl azide, occurs already below 0°C. The resulting carbene dimerizes efficiently even in the presence of alkenes and alkynes to give bis(l,3-dithianylidene) in 78% yield (Scheme 41) <1997T9269>. 

Azirines are also made by carbene addition to nitriles (89 — 90) and by thermal or photochemical (68JA2869) elimination of N2 from vinyl azides (e.g. 91 — 92). Vinyl azides are prepared by the Hassner reaction (68JOC2686, 71ACR9), where iodine azide is first added to an alkene and the resultant (3-iodoazide is dehydrohalogenated with base (Scheme 37) (86RTC456). 

The efficient azidobromination of cycloalkenes [Eq. (5.342)] and open-chain alkenes to give /3-bromoalkyl azides with iV-bromosuccinimide and azidotrimethylsi-lane is catalyzed by Nafion-H.919 Terminal alkenes and alkenes with bulky substituents do not react, whereas 2,3-trimethylbutene-2 reacts without catalysis. The stereochemistry of the process suggests the involvement of a bromonium ion intermediate. 

Davies MJ, Gilbert BC (1984) Electron spin resonance studies, part 68. Addition versus overall one-electron abstraction in the oxidation of alkenes and dienes by S04, Cl2, and OH in acidic aqueous solution. J Chem Soc Perkin Trans 2 1809-1815 Deeble DJ, Parsons BJ, Johnson GRA (1990) Reactions of the hydrogen atom with azide, bromide and iodide ions in aqueous solution. Radiat Phys Chem 36 487-491 Eibenberger FI, Steenken S, O Neill P, Schulte-Frohlinde D (1978) Pulse radiolysis and E.S.R. studies concerning the reaction of S04" with alcohols and ethers in aqueous solution. J Phys Chem 82 749-750... 

A straightforward synthesis of aziridines from electron-rich azide R-N3 (R = alkyl or aryl), electron-deficient alkene, and triflic acid in cold acetonitrile has been reported. The only byproduct was dinitrogen (N2).143... 

Applications of organomercuiy compounds in synthesis overwhelmingly concern Markovnikov conversion of alkenes, allenes and cyclopropanes to alcohols, ethers, amines, peroxides and azides by... 

These iminosilanes react with H-acid compounds like water and ethanol by insertion into the O-H bond, with acetone and 2,3-dimethyl-1,3-butadiene to give alkenes, and with methacrolein, ethylvinylether, silyl and aryl azides to give cycloadducts. 

Covalent azides add to alkenes in a [2 + 3] cycloaddition, giving triazolines (Volume 4, Chapter 4.10), and these in turn can be thermolyzed or photolyzed with loss of nitrogen to give aziridines. The addition obeys the complementarity principle for cycloadditions, which in this case means that electron-rich azides prefer to react with electron-poor alkenes and vice versa. Thus, a few N-alkylaziiidines have been prepared from electron-poor alkenes via triazolines. The thermal stability of triazolines with respect to loss of nitrogen and aziridine formation varies with the electronegativity of the exocyclic N-sub-stituent. Thus, V-vinyltriazolines decompose more readily than N-alkyltriazolines to give V-vinylaziridines in good yield, as in Scheme 18. Several examples of intramolecular formation of... 

Bromine azide, prepared by different methods, undergoes addition to alkenes stereoselectively by an ionic mechanism 33- 37 (Table 2). Improved yields are obtained by using azidotrimethyl-silane and A-bromosuccinimide (NBS) in the presence of Nafion-FI as catalyst33. Alternatively, A-bromosuccinimide may be added to the mixture of the alkene and sodium azide in dimeth-oxyethane/water34. Aziridines were prepared stereoselectively by reduction of (i-bromo azides with lithium aluminum hydride34. 

The reaction of alkenes with iodosobenzene in acetic acid in the presence of sodium azide offers a simple and high yield route to 1,2-diazides (Table 3)76. a-Azido ketones are side products or the exclusive product from the reaction with conjugated alkenes. Allylic azides or oxonitriles, resulting from oxidative cleavage of the C-C double bond, are alternatively obtained from trisubstituted steroid alkenes77. 

An important synthetic route to aziridines is the decomposition of organic azides to the correspondic nitrenes by loss of nitrogen. However, depending on the nature of both, the azide and the alkene and on the experimental conditions, the 1,3-cycloaddition of the azide group to the alkene double bond may occur to give a dihydro triazole, which can be converted in situ or after isolation to the aziridine. Furthermore, /3-functionalized amines are obtained from certain dihydro triazoles, or directly by reaction of azides with certain alkenes, and dihydropyrroles are obtained by reaction of azides with dienes, hence these topics will be treated separately (Section 7.2.9). 

The reaction mechanism is dependent on the nature of both the alkene and the aryl azide. For example, from indene, the imine was obtained by reaction with phenyl azide at 80 °C via the intermediate dihydrotriazole68, whereas with 4-methoxyphenyl azide at 130°C, the aziridine 3 was obtained directly by a concerted mechanism involving loss of nitrogen from the azide71. 

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