Reduction aromatic azides

This approach has been recently extended to the reduction of aromatic azides using EtsSiH, which afford anilinosilanes and hence the corresponding anilines in virtually quantitative yields (Reaction 38). The EtsSi radical adds to the aromatic azido group to give an N-silylarylaminyl radical presumably through loss of nitrogen. Eventual reduction of the silylarylaminyl radical by ferf-dodecanethiol affords N-silylaniline 31, the hydrolytic precursors of the final anilines. 

Reduction of aromatic azides. Aromatic azides can be reduced to anilines by this reagent in CHCl3 at 25°. The rate is accelerated by electron-withdrawing substituents but is reduced by electron-attracting groups. Even so, the presence of an azide group does not interfere with use of the reagent for reduction-of acid chlorides to aldehydes. 

Warrier, M., M.K.F. Lo, H. Monbouquette and M.A. Garcia-Garibay (2004). Photocatalytic reduction of aromatic azides to amines using CdS and CdSe nanoparticles. Photochemical and Photobiological Sciences, 3(9), 859-863. 

Protocol 6 shows the chemoselective reduction of the more electrophilic aromatic azide. Reaction of the resultant IMP with phenyl isocyanate gives the carbodiimide, which upon heating in a sealed tube, undergoes cyclization. 

The reduction of aromatic azides " is carried out by refluxing 0.1 mole of the azide with 0.072 mole of sodium borohydride in 100 ml. of isopropanol for 2 hrs. For aliphatic azides it seems to be necessary to use a larger excess of the metal hydride and a longer reaction time. The azide I (2.84 mmoles) and sodium borohydride (6.61 mmoles) are heated together in 10 ml. of refluxing isopropanol for... 

Again, no reaction was observed in the absence of mercaptoethanol. The mechanistic steps for the transformation were elucidated by the Chatgilialoglu et ah and are represented in Scheme 4.13, in analogy with the pathway reported for the radical reduction of aromatic azides with triethylsilane in toluene, with the addition of silyl radicals to the azide function, liberation of nitrogen and formation of silyl-substituted aminyl radical. The thiol is the hydrogen atom donor to this intermediate and it can be regenerated by its interaction with the silane, thus propagating the chain. The hydrolysis of the silylamine occurred... 

In neutral media, they leave carbonyl derivatives intact but reduce tosylhydrazones to the corresponding hydrocarbons under reflux of CHCI3 (Section 3.3.4). This reduction is compatible with a-enone, epoxide, or lactone groups present in the molecule [GL3]. In cold acetone, these reagents reduce acid chlorides to aldehydes [FHl] (Section 3.2.7). In the presence of Lewis acids or gaseous HCl in CHjClj, they reduce aldehydes and ketones. The selective reduction of aldehydes in the presence of ketones can also be realized (Section 3.2.1). These reagents also reduce aromatic azides to amines (Section 5.2). 

Bakers yeast catalyzes the reduction of azides and nitro compounds to amines128 2911. For example, it catalyzes chemoselective reduction of azidoarenes to arenamines as shown in Fig. 15-50[286, 287). Excellent yields are obtained for various aromatic compounds on reaction at room temperature. Aromatic nitro compounds... 

The reduction of azides to amines proceeds in low yield under usual conditions, but it can be performed efficiently under phase-transfer conditions, using NaBH4 supported on an ion-exchange resin, or using a THF-MeOH mixed solvent (this last method is well suited only for aromatic azides). ... 

As reported in 1902, the substrate scope of the Dimroth triazole synthesis was limited to aromatic azides. An early extension of this methodology was reported in 1956 by Hoover and Day at the University of Pennsylvania. IH-1,2,3-Triazoles were of particular interest at the time as potential modifiers of nucleic acid metabolism. As part of a program directed at cancer chemotherapies, they replaced the azide aromatic moiety with a benzyl substituent. Sodium ethoxide-promoted reaction of benzyl azide (19) with active methylene compounds 25 provided 1-benzyl-1,2,3-triazoles 26 that could undergo reductive cleavage with sodium in liquid ammonia to afford the desired 4,5-disubstituted species. While various active methylene compounds were successfully used (ethyl cyanoacetate, cyanoacetamide, cyanoacetic acid, and malononitrile), the yields were low to modest when compared with aromatic substrates. ... 

Benati, L. Bencivenni, G. Leardini, R. Minozzi, M. Nanni, D. Scialpi, R. Spagnolo, R Zanardi, G. Radical reduction of aromatic azides to amines with triethylsilane. J. Org. Ghent. 2006, 71, 5822-5825. 

Keywords Aromatic azides, BF3.0Et2/NaI, MeCN, room temperature, selective reduction, amines, reductive-cyclization, pyrrolo[2,l-c][l,4]benzodiazepines... 

In combination with sodium iodide, Al(OTf)3 catalyzed the reduction of aromatic azides to the corresponding amines. This methodology was chemoselective for aryl azides and proceeded in shorter reaction times than common strategies (eq 17). ... 

Scheme 4-342. Iron-catalyzed reduction of aromatic azides.

A novel method for preparing amino heterocycles is illustrated by the preparation of 2-amino-5-methylthiophene (159). In this approach vinyl azides act as NH2 equivalents in reaction with aromatic or heteroaromatic lithium derivatives (82TL699). A further variant for the preparation of amino heterocycles is by azide reduction the latter compounds are obtained by reaction of lithio derivatives with p- toluenesulfonyl azide and decomposition of the resulting lithium salt with tetrasodium pyrophosphate (Scheme 66) (82JOC3177). 

Hydriodic acid is a reagent of choice for reduction of alcohols [225], some phenols [225], some ketones [227, 228], quinones [222], halogen derivatives [22S, 229], sulfonyl chlorides [230], diazo ketones [231], azides [232], and even some carbon-carbon double bonds [233]. Under very drastic conditions at high temperatmes even polynuclear aromatics and carboxylic acids can be reduced to saturated hydrocarbons but such reactions are hardly ever used nowadays. 

Neither aromatic halogens [232,602] nor nitro groups were affected during the reductions of the azido group [232, 247, 602]. a-Iodo azides gave, on reduction, aziridines or alkenes depending on the substituents and on the reagents used [603]. 

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