Hydrazoic acid, additions double bonds

A surface-mediated (SiC>2 or AI2O3) addition of hydrazoic acid, generated in situ from Me3SiN3 and CF3SO3H, to 1-methylcyclohexene and 1,2-dimethylcyclohexene has been reported69. The reaction obeys the Markovnikov rule and is therefore believed to proceed via the initial protonation of the double bond to generate a carbocation. This mechanism is also supported by the observed non-stereospecificity69. 

Hydrazoic acid adds readily to alkenes which are conjugated to powerful electron-withdrawing groups. Since such groups reduce the basicity of the carbon-carbon double bond, electrophilic attack by hydrazoic acid is more difficult, so that where reaction occurs it is likely to proceed by nucleophUic attack. The best known examples are the additions to a,/3-unsaturated carbonyl compounds and these are discussed subsequendy. 

The difference is interestingly exemplified in the differing modes of reaction of hydrazoic acid with some alkylidene (and arylidene) oxazolone derivativesThe alkylidene compound 174 behaves as an a, -unsaturated carbonyl compound with the hydrazoic acid adding to the exocyclic double bond. A subsequent ring opening with further addition leads to the formation of the diazide 175 (equation 75). In contrast the exocyclic double bond of the arylidene compound 176 is unreactive, and nucleophilic attack occurs at the... 

Because of the weakness of hydrazoic acid as a potential electrophilic reagent one would expect electrophilic addition of hydrazoic acid only in systems in which a powerful electron-releasing group is conjugated with the double bond. An interesting example of such an... 

The pattern of addition in polyenes in which the double bonds are neither contiguous nor conjugated does not require special comment. Compounds with conjugated double bonds are somewhat more susceptible to electrophilic addition than simple alkenes but nevertheless there appear to be no literature reports of such compounds undergoing addition reactions with hydrazoic acid in the absence of a catalyst. 

Additions of hydrazoic acid to carbon-sulphur double bonds may conceivably be of the general type outlined in equation (88) but do not constitute a synthetic route to azides. Recent corrections to the earlier literature relating to this field are, however, noteworthy. It was originally suggested that thiocarbamoyl azides " (193) were obtained from organic isothiocyanates and hydrazoic acid. The spectroscopic studies of Lieber and co-workers " have now established that the products are in fact thiatriazoles (194). The reactions of sodium azide with isothiocyanates , and carbon disulphide , which were also previously considered to furnish organic azides, have now been shown to produce the heterocyclic compounds 195 and 196 respectively. 

In this chapter, we first describe the successful methods for the hydroazidation of a,P-unsaturated carbonyl compounds. The classic approach for the addition of hydrazoic acid and its derivatives onto non-activated double bonds is then examined. In the last section, we present our own work in this area and our progress towards a general method for the hydroazidation of olefins. 

In 1915, Oliveri-Mandala first reported on the conjugate addition of hydrazoic acid onto a quinone derivative, but the product obtained was an aromatic azide. The first real hydroazidation reaction of electron-deficient double bond was then reported... 

The hydrohydrazination represented a general solution for the amination of alkenes, but the protected hydrazines obtained are sometimes difficult to transform to the free amines. At this point, we turned to sulfonyl azides as nitrogen sources, based on then-capacity to react both with enolates and carbon-centered radicals. Mechanistic investigations of the hydrohydrazination reaction had suggested a radical character for the formed organocobalt intermediate. " We were pleased to see that the Cobalt-catalyst 4 was able to promote the hydroazidation of 4-phenylbut-l-ene (3) with ethanesulfonyl azide (7), giving the product derived from the formal Markovnikov addition of hydrazoic acid onto the C-C double bond exclusively, albeit in moderate yields (50%). 

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