Oximes, azido

N, C -Coupling reaction of BENA with trimethylsilyl azide is the key step of a very convenient and versatile procedure for the synthesis of otherwise difficultly accessible a-azido oximes (524, 525) (Scheme 3.248). 

Both terminal and internal BENAs (434) are readily subjected to this transformation to give the a-azido oximes (465) in very high yields. The improved procedure allows one to prepare compounds (465) virtually without by-products. The use of a large excess of silyl azide and the presence of small additives of triethylamine (5%) are of principal importance. 

As can be seen in Scheme 3.249, a-azido oximes (465) can be involved with advantage in the selective reduction of the azido group in the presence of the oximino fragment and also in the selective or nonselective reduction of the oximino fragment (525). 

Due to these procedures as well as to some other transformations, the a-azido oximes can be considered as efficient basic reagents in the synthesis of various derivatives of 1,2-disubstituted ethanes using readily available AN (431) as starting compounds. 

Oxidation is a general method for the preparation of nitro sugars from other sugar derivatives, as amino or azido sugars and sugar oximes. 

Azidoacetaldehyde, 0772 Azidoacetic acid, 0774 Azidoacetone, 1190 Azidoacetone oxime, 1215 2,5-Diazido-3,6-dichlorobenzoquinone, 2054 Ethyl -azido-A-cyanophenylacetim idatc. 3397 Ethyl 2-azido-2-propenoate, 1890 Ethyl 2,3-diazidopropionate, 1903 Tetraazido-l,4-benzoquinone, 2633 See 2-AZIDO-2-FLUOROCARBOXYLATES... 

Acetohydrazide, 0912 Acetone oxime, 1258 Acetylenedicarboxylic acid, 1405 Acrylaldehyde, 1145 f Allyl acetate, 1912 A-Ally lthiourca. 1600 4-Aminophenylazobenzene, 3487 Ammonium dichromate, 4246 Ammonium peroxodisulfate, 4576 4-Azidobenzaldehyde, 2697 2-Azido-2-phenylpropane, 3159 f Aziridine, 0863 Azobenzene, 3483 Azoformamide, 0816 Azoisobutyronitrile, 3011 Azoxybenzene, 3485 Benzaldehyde oxime, 2760... 

Treatment of (7-acylated azido oximes (care ) with triphenylphosphane affords iminophos-phoranes, which undergo intramolecular Staudinger reaction to oxadiazoles (Scheme 45) <86S843>. 

Various nitrosoarenes have been utilized as benzofurazan precursors including o-azido derivatives generated from the o-chloro analogues <66JCS(B)1004>, and 1-amino-2-nitrosoarenes which can be oxidized with ferricyanide or hypochlorite. Treatment of o-nitrosophenols with hydroxylamine also affords the furazan, presumably via an oximation-dehydration pathway involving the tautomeric o-quinone monooxime. Other related approaches involve the reduction of o-dinitroarenes with borohydride, and the thermolysis of o-nitroanilines and o-nitroacetanilides. 

Azidoacetaldehyde, 0768 Azidoacetic acid, 0770 Azidoacetone oxime, 1211 Azidoacetonitrile, 0710 Azidoacetyl chloride, 0689 4-Azidobenzaldehyde, 2693 Azidobenzene, see Phenyl azide, 2264 7-Azidobicyclo[2.2.1]hepta-2,5-diene, 2773 2-Azido-1,3-butadiene, 1468 Azido-2-butyne, 1469... 

Acetohydrazide, 0908 Acetone oxime, 1254 Acetylenedicarboxylic acid, 1401 f Acrylaldehyde, 1142 f Allyl acetate, 1906 iV-Allylthiourea, 1595 4-Aminophenylazobenzene, 3481 Ammonium dichromate, 4240 Ammonium peroxodisulfate, 4571 2-Azido-2-phenylpropane, 3154... 

Reduction of saturated l-oximino-5a-steroids with usual reagents gives the la-amino-derivatives. The previously unknown 1/3-amino-compounds have now been obtained by reduction of the A2-unsaturated 1-oxime. Hydrogenation (Pt-H2) leads to the saturated la- and 1/3-amines directly, while zinc-acetic acid gave the unsaturated amines which could be hydrogenated in a separate step to give the saturated amines.197 The four isomeric 16-azido-17-alcohols, and thence the 16-amino-17-alcohols, have been prepared by the routes indicated in Scheme 8 [3-methoxyoestra-l,3,5(10)-triene series]. The 16/3,17/3-epoxide gave a mixture of two tra/ts-azido-alcohols.198... 

Analogously with the reaction depicted in equation (37), a-N-morpholino oxime (59) underwent oxidative ring cleavage under standard Beckmann conditions (equation 39). Azide nitrogen assisted cleavage of the steroidal azido oxime (60) gave a dinitrile (equation 40). ... 

In a similar way to azidoazomethines, the corresponding azido oximes and hydrazides may be obtained (Scheme 43). The formation of cyclic tautomers seems to play only a minor role here." The stereochemical aspects of the transformation of 0-acylhydroxamoyl chlorides (33 R = "Ac) with N3 ions have been studied by Hegarty. Further systems such as the interesting pairs guanyl azides (34)/5-aminotetrazoles, are comprehensively discussed by Lwowski. ... 

To date, four bioorthogonal reactions have been used to label glycans on cells and in lysates hydrazone/oxime formation with ketones, thiol alkylation with maleimides, Staudinger ligation of azides with triaryl phosphines, and copper-catalyzed or strain-promoted [3+2] cycloadditions of alkynes and azides (Figure 5) (25, 26, 32, 34, 35). While each reaction has been used extensively, most recent applications have employed azido- or alkynyl-sugars due to their superior metabolic incorporation and efficient ligations. 

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