A-Aryl vinyl azides

Various a-aryl vinyl azides and internal alkynes were transformed into highly substituted isoquinolines under the [Cp RhCl2]2-Cu(OAc)2 bimetallic catalytic system in DMF as the solvent (eq A) ... 

Wang et al. obtained the same isoquinoline 111 by treatment of a-arylated vinyl azide 112 in the presence of a rhodium/copper catalyst system (Scheme 25.55) [53]. 

Three recent publications dealing with a-imino azides °, a-azido chloridcs and vinyl azides reflect the utility of infrared measurements with alkyl and aryl azides. 

The decomposition of organic azides has been studied from a number of points of view, the objectives being mainly synthetic or mechanistic. The nature of the intermediates formed have received much attention. In this chapter we shall consider the decomposition of alkyl, aryl and sulphonyl azides under various conditions. Acyl and vinyl azides are considered elsewhere in this volume. 

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 mechanism of azirine formation has been discussed by L abbe.20 A priori, the three paths shown in Scheme 1 can be considered. From a comparison of the activation parameters27 for vinyl azide decomposition ( a 26-30 kcal/mol, AS - 3 to + 5 eu) with those for aryl azides (Ea 35-39, AS 18) it appears that the nitrene pathway a can be excluded, but a clear choice between paths b and c cannot be made at this time.20... 

Vinyl Azides. Vinyl azides such as 37 or 38 react with alkyl-, aryl-, and heteroaryllithium reagents like other azides to give the corresponding triazenes. Hydrolysis of the latter leads to nitrogen-free carbonyl compounds when aliphatic lithium reagents are used (path A, Eq. 28),277 but when benzyl, aromatic, and heteroaromatic lithium reagents are used, amines are formed in fair to good yields (path B).278... 

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. 

Aryl and vinyl azides can also be accessed in one step from the corresponding halides or triflates via a copper-catalyzed reaction with sodium azide in the presence of a catalytic amount of L-proline (Scheme 7.5C) [104]. In this fashion, a range of 1,4-disubstituted 1,2,3-triazoles can be prepared in excellent yields [105-107]. Anilines can also be converted to aryl azides by the reaction with tert-butyl nitrite and azidotrimethylsilane [108]. The resulting azides can be submitted to the CuAAC conditions without isolation, furnishing triazole products in excellent yields. Microwave heating further improves both reactions, significantly reducing reaction time [56, 62]. 

The question now arises as to whether the Chapman mechanism is applicable to the decomposition of other aryl azides. Bicyclic aryl azides, for example, have a considerable degree of double-bond fixation in their aromatic rings. This might be expected to make them behave more like vinyl azides, which are known to give azirines on photolysis. It is therefore useful to compare the nature of the products formed on photolysis in nucleophilic solvents by a series of azides that have an increasing degree of vinyl azide character ... 

On evidence currently available, it may be said that a didehydroazepine is as likely as an azirine to be the intermediate that undergoes nucleophilic attack in bicyclic aryl azide decompositions and is probably the preferred intermediate when dealing with monocyclic aryl azides. An exception to this generalization occurs when the azide decomposed contains vinyl azide character, for example 9-azidophenanthrene and 6-azido-l,3-dimethyluracil (Section II.3.A), in these cases azirines are almost certainly the reactive species. 

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

Scheme 11.13 Pyrolysis of a-aryl substituted vinyl azides ...

Bolm and coworkers have developed a new route to the synthesis of indole derivatives by Fe(OTf)2-catalyzed intramolecular C(sp )-H amination reaction of azidoacrylates (Scheme 9.3) [5]. This method proceeds through the amination of a vinyl azide with an aryl C(sp )-H bond, and the iron catalytic system is efficient... 

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