Alkenyl azides

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. 

See also Lithium azide Alkyl nitrates, etc., also NITRATING agents (reference 3) See related ALKENYL NITRATES... 

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. 

Other cycloadditions were reported. The intramolecular cycloaddition of alkenylnitrones was 2q>phed to the synthesis of piperidines <99TL1397, 99JCS(P1)185>. Cycloaddition of an alkenyl azide afforded piperidines after reduction of the bicyclo triazole <99T1043, 99EJOC1407>. Similar to the cyclization of the diazo imide 2 in section 6.1.2.1, isomiinchnone intermediates can rearrange to functionalized piperidines <99JOCS56>. 

SCHEME 20. Preparation of an alkenyl zinc reagent bearing an azide function... 

The chemistry of alkyl and alkenyl azides has been well summarized in several recent reviews.233-237 The azides can be prepared via numerous methods, of which the addition of hydrazoic acid to C—C multiple bonds is one. With the exception of cyclopropenes,238 most alkenes are unreactive towards hydrazoic acid itself. However, the addition can be catalyzed by acids (phosphoric acid,239 sulfuric acid260 or trifluoroacetic acid261) or Lewis acids (aluminum trichloride, boron trifluoride or titanium tetrachloride).262... 

The alkenyl group of an azidoalkene is always attached to the end of the 1,3-dipole. Only 1,3-cycliza-tions have been observed with azides, typically giving fused bicyclic systems. 

A wide range of organic azides such as alkyl,80 alkenyl,79,100 aryl, including dinitrophenyl and picryl,101-103 heterocyclic,28,91 trimethylsilyl,79,104 acyl,9 phosphoryl,105 sulfonyl,106 alkoxycarbonyl,9 and oxime azides107 has been found to add to norbornene,25,79,90,104,105,107-121 its derivatives,104 106,1 13,120,122-128 or to related bridged bicyclic... 

R2 = H, alkyl, or alkenyl, using aryl,409,411,412 acyl,407,410 414 alkoxycar-bonyl,410,412,415 vinyl,416 and tosyl411 azides. 

A mixture of diastereomeric azides (E/Z) in fast equilibrium (III, Fig. 19) has been obtained by treatment of 3-alkenyl-3-bromoazetidin-2-ones with NaN3 [291]. The subsequent hydrogenation and the following protection with CBz derivatives afforded 3-(2 -amino)-(3-lactams as single diastereomers (IV, Fig. 19). 

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. 

Microporous superbasic catalysts based on zeolites suitable for alkene isomerization were developed by Martens et al. [28-30]. They have high activity in the 1-butene isomerization and side-chain alkenylation of xylene [31], and are prepared by impregnating a dehydrated zeolite (NaY) with NaN3 in alcoholic solution. Subsequent decomposition of the azide inside the zeolite pores produces metallic sodium particles Nax°and cationic sodium clusters Na43+. The high catalytic activity was attributed to the ionic sodium clusters as they could be detected using ESR spectroscopy. 

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). 

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. 

Aldol condensation, 111, 249 Aldoximes, 41, 42, 383 Alkali acetylides, 166 Alkamines, 261 Alkenyl bromides, 254 Alkyl azides, 403, 404 9-Alkylbicyclo[3.3.1JnonanoI-9, 31 Alkyl bromides, 254 Alkyl fluorides, 136 Alkyl halides, 133, 378 5-Alkyloxazolidones, 122 Alkylsulfenes, 103 Alkynes, 141, 248, 249 Alkynes, trimerization, 23 Allene, 388 AHenes, 274-276, 465 Allenyl ethers, 337 Allyl alcohol, 415 Allyl alcohols, 4)5 Allylailenes, 52 Allylamines, 326 Allyl bromide, 324 Allylcarbinyl chloride, 463 Allyl chloride, 109 Allyl ethers, 158... 

An alkynyl azide such as (373) is thermolytically converted into a pyrimidine alkenyl azides similarly yield dihydro products. 

Mercury, Zinc, and Copper. The thermal decomposition of 2-thienylmercury thiocyanate, azide, acetate, and trifluoromethylsulphonate has been investigated. Thienylmercury derivatives have been cross-coupled with primary and secondary alkyl- and alkenyl-cuprate reagents. 2-Thienylzinc chloride has been coupled with iodobenzene and vinyl bromide, using Pd catalysis. ... 

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

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