Alkenyl azides reactions

Azides are highly valuable radical acceptors that form nitrogen-centered radicals after addition onto them, as in the case of the transformation of 31 into 32. This reaction opens new possibilities for making pyrrolidines. Murphy, for instance, disclosed the synthesis of ( )-horsfihne and ( )-coerulescine by tandem cyclization of iodoaryl alkenyl azides such as 29 [42]. By the same strategy and using precursor 33, formal syntheses of ( )-vindohne [43] and ( )-aspidospermidine [44] have been rendered possible (Scheme 10). 

Z -1-Alkenyl azides have been prepared by the regio- and stereo-selective reaction of trans-1,2-epoxyalkylsilanes with... 

Azanaphthalene iV-oxides undergo photochemical deoxygenation reactions in benzene containing BF3 OEt2, resulting in amines in 70-80% yield these amines are important in the synthesis of heterocyclic compounds. Azidotrimethylsilane reacts with traws-1,2-epoxy alky Isilanes in the presence of BF3-OEt2 to produce (Z)-l-alkenyl azides. The cis-1,2-epoxyalkylsilanes undergo rapid polymerization in the presence of Lewis acids. 

The copper-catalyzed reaction of j8-styrylboronic acid with sodium azide afforded ( )-j8-styryl azide in good yield. In rare cases, the rearrangement of butatrienylidene and alkynyl complexes of iridium led to special enazides. A single example of the formation of an alkenyl azide via palladium-catalyzed cyclization of an allenic substrate has also been reported. ... 

Cheletropic additions at the C,C double bond of alkenyl azides, for example, reactions with carbenes to generate azidocyclopropanes or epoxidation are weU-known for several decades. Recently, the 1,4-addition of sulfur dioxide to 2-azidobuta-l,3-dienes 92 has been investigated (Scheme 5.27). Moderate yields of the corresponding 3-sulfolenes 226 were obtained. 

However, the formation of the pyrroles 234 by copper(II)-catalyzed reaction of alkenyl azides 229 with ethyl acetoacetate was explained by an attack of the enolate 231 at the jS-carbon atom of the polarized C,C double bond of intermediate 230 (Scheme 5.29). The proposed mechanism included ring closure by a second nucleophilic attack followed by hydrolysis, dehydration, and tautomerism to get the aromatic final product 234. 

A second group of aromatic substitution reactions involves aryl diazonium ions. As for electrophilic aromatic substitution, many of the reactions of aromatic diazonium ions date to the nineteenth century. There have continued to be methodological developments for substitution reactions of diazonium intermediates. These reactions provide routes to aryl halides, cyanides, and azides, phenols, and in some cases to alkenyl derivatives. 

For intramolecular 1,3-dipolar cycloadditions, the application of nitrones and nitrile oxides is by far most common. However, in increasing frequency, cases intramolecular reactions of azomethine ylides (76,77,242-246) and azides (247-259) are being reported. The previously described intermolecular approach developed by Harwood and co-workers (76,77) has been extended to also include intramolecular reactions. The reaction of the chiral template 147 with the alkenyl aldehyde 148 led to the formation of the azomethine ylide 149, which underwent an intramolecular 1,3-dipolar cycloaddition to furnish 150 (Scheme 12.49). The reaction was found to proceed with high diastereoselectivity, as only one diaster-eomer of 150 was formed. By a reduction of 150, the proline derivative 151 was obtained. 

Recent progress on the use of hypervalent iodine reagents for the construction of carbon-het-eroatom (N, O, P, S, Se, Te, X) bonds is reviewed. Reactions of aryl-A3-iodanes with organic substrates are considered first and are loosely organized by functional group, separate sections being devoted to carbon-azide and carbon-fluorine bond formation. Arylations and alkenyla-tions of nucleophilic species with diaryliodonium and alkenyl(aryl)iodonium salts, and a variety of transformations of alkynyl(aryl)iodonium salts with heteroatom nucleophiles are then detailed. Finally, the use of sulfonyliminoiodanes as aziridination and amidation reagents, and reactions of iodonium enolates formally derived from monoketones are summarized. 

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. 

These reactions include the well known additions to alkynyl- and alkenyl-phospho-rus(V) acids of diazomethane and other diazoalkanes, and also of azides, either inter- or intra-molecularly. 

Triazole Derivatives. Triazole derivatives are known to possess tumor necrosis factor-a (TNF-a) production inhibitor activity. The synthesis of triazole derivatives can be achieved from alkynes or diynes by a tandem cascade reaction involving 1,3-dipolar cycloaddition, anionic cyclization and sigmatropic rearrangement on reaction with sodium azide. Some of the benzoyl triazole derivatives were considered to be potent local anaesthetics and are comparable with Lidocaine. The triazoles can also be prepared from benzoyl acetylenes,triazoloquina-zoline derivatives, 2-trifluoromethyl chromones, aliphatic alkynes, 2-nitroazobenzenes, ring opening of [ 1,2,4]triazolo [5,1-c] [2,4]benzothiazepin-10 (5//)-one, alkenyl esters and dendrimers. A number of these reactions are outlined in eqs 44 8. 

Both alkyl and alkenyl amino acids can be prepared by this approach. A common method for introducing the halide into an alkene-bearing molecule is illustrated by the reaction of -pent-2-enoic acid with N-bromosuccinimide to form 1.12. Subsequent treatment with ammonia led to displacement of the bromine moiety to give 4-aminopent-2-enoic acid (J.I3). An alternative method reacted 1.12 with sodium azide and then reduced the azide with zinc and acetic acid (see section l.l.B.iv). Allylic halogenation in systems such as 1.12 are well known. 

Perfluoropropene and perfluorobutene-2 react with benzyl azide at 150 °C to give the [3+2] cycloadducts in 85% and 65% yields, respectively. Trimethylvinylsilane also undergoes the [3+2] cycloaddition reaction with 4-nitrophenyl- and 4-cyanophenyl azide to give the triazolines in high yields. Also, ]V-alkylmaleimides react with trimethylsilyl azide to give the corresponding [3+2] cycloadduct . The reaction of maleimide A -proponic acid and a heterocyclic azide is accelerated by molecular recognition . The palladium-catalyzed reaction of alkenyl bromides with sodium azide in dioxane at 90 °C or DMSO at 110 °C affords the 4-substituted 1,2,3-triazoles 55. ... 

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