Aryl substituted azides

Since there are numerous examples of benzenes substituted with one azido group known, we will only take into consideration the much smaller number of compounds containing two or more azido groups, or molecules containing more than one azidoaryl group. 

Some 1,3-diazidobenzene derivatives were prepared by double diazotation of the corresponding diaminobenzenes in low yields and studied for the purpose of dinitrene 

The only structurally characterized benzene containing three azido groups is the sym-triazidotrinitrobenzene (molecular structure shown in a recent review ), a surprisingly easy to handle, long-known material. 

The only report about a higher azide eontaining (penta- and hexasubstitution) benzene as a minor produet is from a treatment of hexafluorobenzene with sodium azide and its stepwise substitution of fluorine by azide. The major products from this reaction reportedly were those of di- and tetra-substitution, C6F4(N3)2 and C6F2(N3)4, but no further details are available. 

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It was recently suggested that for alkyl or aryl substituted azides, most agreed that the concerted mechanism was likely the case. However, when salts of hydrazoic acid are used (as ionic azide is not a 1,3-dipole), or when a strongly EWG is attached to the nitrile, many authors still favor the stepwise process based on computational and experimental evaluation. ... 

The thermolysis of aryl azides in alcoholic solution has been used to prepare 2-alkoxy-37f-azepines. Thermolysis of 3-azidophenyl methyl ketone in methanol in a sealed ampule furnishes a mixture of the 6-acetyl- (36a) and 4-acetyl-2-methoxy-3//-azepine (37a) in superior yields to those obtained in the corresponding photolytic reaction.78 Other 3-substituted azides behave similarly, with a preference for the 6-substituted isomers 36, as is observed for azide photolyses in amine solutions. 

Practicable yields of 5-substituted 2-methoxy-3//-azepines 94 can be obtained by photolysis of aryl azides 56 bearing an electron-withdrawing group para to the azide function, although irradiation times tend to be longer and, in general, yields lower than with the corresponding 2-substituted azides.197... 

Substituted anhydro-5-hydroxy-l,2,3,4-oxatriazolium hydroxides (4) decompose on heating in strong acids <320912,56JA5124>. The 3-alkyl substituted compounds produce carbon dioxide, azo-imide (HN3), and the alcohol corresponding to the 3-substituent. The 3-aryl substituted analogues produce carbon dioxide and aryl azide. In some cases the initially formed aryl azide decomposes further to anilines under the conditions of the reaction <82JCS(P2)70l>. Kinetic studies indicate that 3-methyl-anhydro-5-hydroxy-l,2,3,4-oxatriazolium hydroxide (24) reacts via a bimolecular A-2... 

The photochemistry of 3-aryl-substituted l,4,2-dioxazol-2-in-5-ones (79) can be interpreted in terms of ring cleavage and loss of carbon dioxide with the formation of an acyl nitrene (80) such nitrenes are also formed by the photolysis of acid azides. In dimethyl sulfide, therefore, the 3-phenyl derivative itself (79 Ar=Ph) is converted into the photoproduct (81).05 When the phenyl group is substituted in... 

Silyl Azides. Many of these compns are extremely unstable and several of the aryl substituted compds such as phenyltriazidosilane (C6HsN9Si) deton on handling (Refs 17 18). 

The procedure is essentially similar to that described for the preparation of 5-amino-l,2,3,4-thiatriazole. Freund and Hempel6,7 have reported observing that the initial diazotization products of 4-aryl-substituted thiosemicarba-zides lead to the formation of tetrazoles, while the corresponding 4-alkyl-substituted thiosemicarbazides were considered by Freund and Schwarz8 to be thiatriazoles. However, Oliveri-Mandala,9 on the basis of his study of the reaction of alkyl and aryl isothiocyanates with hydrazoic acid, concluded that the initial diazotization product of either 4-aryl or 4-alkyl thiosemicarbazides were open-chain thiocarbamyl azides, RNHC( S)N3. Lieber, Pillai, and Hites10 have recently clarified this situation and have shown... 

A useful, although somewhat limited, method of preparing vinyl azides involves the addition of azide ion to vinyl halides with subsequent elimination of halide ion. This reaction is only possible when the halogen is located to a group which can effectively stabilize the intermediate carbanion. A number of alkyl and aryl substituted )3-chlorovinyl ketones (23) have been found to react in this way ". In many cases, however, the resulting /3-azidovinyl ketones (26) cannot... 

The alkyl- and aryl-substituted vinyl azides discussed above are all reasonably stable at room temperature. However, the introduction of strongly electron-withdrawing substituents on the double bond appears to facilitate thermal decomposition of these compounds. A number of azides thus substituted have been found to decompose at room temperature or belo. v. 

The simplest member of the class of vinyl azides, H2C=CH-N3, has been known for about 100 years. However, it was not until the late 1960s that vinyl azides became an important and synthetically useful class of organic compound. The most interesting and important reaction of vinyl azides is the formation of azirines produced upon photolysis and thermolysis of vinyl azides. Smolinsky and Pryde first observed azirine formation, together with a small amount of keteneimine, by gas-phase pyrolysis of a-aryl-substituted vinyl azides. 

As noted above, most kinetic studies of alkene radical cations in solution have focused on aryl-substituted systems since they have convenient optical propenies and have been extensively studied by other techniques. Radical cations are frequently identified on the basis of their characteristic UV-visible absorptions and the comparison of their spectra to those obtained in matrices at low temperature." However, a number of other diagnostic tests are also commonly employed to identify these intermediates. For example, their kinetic behavior as a function of solvent nucleophilicity or added nucleophiles is analogous to that of other electrophilic species. Thus, reaction with nucleophiles such as azide and halide ions provides support for the assignment of a transient to a radical cation, although it will not serve to eliminate a carbocation intermediate. More useful in the latter respect is the method of generation of the transient since PET does not in general lead to the formation of carbocations. Quenching of the observed transient with a more easily oxidized... 

Aryl-substituted aldehydes 352 can be cleaved to chain-shortened carbonyl compounds 353 and formaldehyde by iodosylbenzene in the presence of acids or Lewis acids (Scheme 3.140). Formaldehyde is further oxidized to CO and CO2 under the reaction conditions [457]. Oxidative decarboxylation of 2-aryl-substituted carboxylic acids 354 into corresponding aldehydes, ketones (e.g., 355) and nitriles at room temperature can be achieved by treatment with (diacetoxyiodo)benzene and a catalytic amount of sodium azide in acetonitrile (Scheme 3.141) [458]. 

Substituted aryl sulfonyl azides decompose at elevated temperatures to nitrenes and add to natural rubber ... 

The disadvantage of this method for synthesizing 1-aryl-substituted A -tetrazoline-5-ones is the fact that three equivalents of sodium azide per equivalent isocyanate are required [ 102]. To circumvent this drawback, a process for the generation of 1-aryl- and 1-alkyl-substituted A -tetrazoline-5-ones was developed that uses equimolar amounts of sodium azide, aluminum chloride and the corresponding isocyanate in DMF as solvent. Heating of this three component mixture for 2 to 24 hours followed by treatment with dilute hydrochloric acid provides the 1-aryl- and 1-alkyl-substituted A -tetrazoline-5-ones, respectively [103]. 

Alkyl-, vinyl-, and aryl-substituted acyl azides undergo thermal 1,2-carbon-to-nitrogen migration with extrusion of dinitrogen — the Curtius rearrangement — producing isocyantes. Reaction of the isocyanate products with nucleophiles, often in situ, provides carbamates, ureas, and other A-acyl derivatives. Alternatively, hydrolysis of the isocyanates leads to primary amines. 

Aryl-substituted pyridines and pyrimidines have been prepared by 2 - - 2-cycloadditions of alkynyl-substituted pyridines and pyrimidines with electron-rich dienes." The reactions proceed by formation of a bridged cycloadduct and subsequent thermal extrusion of ethylene. The pyridine moiety plays a crucial role for the success of the reaction. 2-Benzoylbenzoyl azides undergo facile cycUzation under acidic conditions to give substituted dibenzo[ / [l,5]-diazocines in good yields. The mechanism of the diazocine synthesis was assumed to proceed by an unprecedented intermolecular 2 - - 2-cyclization. 

Toste has reported a gold(I)-catalyzed protocol for the intramolecular addition of an alkyl azide to an alkyne with loss of dinitrogen (acetylenic Schmidt reaction) to form pyrrole derivatives [19]. For example, treatment of homopropargyl azide 16 with a catalytic 1 2 mixture of (dppm)Au2Cl2 (dppm = l,2-bis(diphenylphosphino)meth-ane) and AgSbFfi in methylene chloride at 35 °C led to isolation of2,5-dibutylpyrrole in 82% yield (Eq. (11.13)). The method was also effective for the cyclization of a-unsubstituted homopropargyl azides and tolerated both alkyl and aryl substitution of the alkyne. 

Photolysis of aryl azides in the presence of oxygen gives nitro compounds and, in the case of substituted azides, also an azoxy compound ... 

In addition it may be noted that amides of a, 3-unsaturated adds and of a-hydroxyacids yield aldehydes when allowed to undergo this rearrangement. Aryl-substituted semicarbazides yield azides, and aryl--substituted ureas yield aryl-substituted hydrazines. These reactions are discussed more fully in a subsequent section of this chapter (p. 273). 

Another approach to the synthesis of alkyl azides is the use of a phase-transfer catalyst (see Scheme 3.8). For instance, high yields are obtained when alkyl bromides are treated with NaNs in the presence of aUquat 336 . The use of crown ethers has also been described. An illustrative example is the reported synthesis of glycoside derivatives, which explores the mesylate displacanent with sodium azide in 18-crown-6 to give azide 58. More recently the synthesis of alkyl- and aryl-substituted ( )-2-(azidomethyl)alke-noates from the corresponding aUyUc bromides 59 in aqueous acetone has been reported (Scheme 3.8). 

The chemistry of substituted cyclopropanones is even more engagingly complicated. For example, 2,2-dimethylcyclopropanone acetals were shown to react with alkyl azides in the presence of BFs-OEta to afford a-amino-of-diazomethylketones like 12 along with a small amount of 3-azetidinones 13 (Scheme 7.10). Interestingly, aryl-substituted... 

Smolinsky and Pryde first observed azirine formation, together with small amount of ketenimin, by gas-phase pyrolysis of a-aryl substituted vinyl azides. 

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