Nitronium salts amides

The above synthesis has a few noteworthy points. The nitrolysis of bicyclic amides like (67) are frequently problematic in terms of inertness towards nitrolysis and the ease with which ring decomposition occurs. This synthesis is an interesting balancing act. Ring decomposition results when the bicycle (67) is treated with absolute nitric acid, mixed acid or nitronium salts. When the diacetyl equivalent of the bicycle (67) is treated with dinitrogen pentoxide-absolute nitric acid-TFAA reagent, the yield drops to 10 %. 

Nitronium salts as discussed react extremely readily with ir-donor aromatic compounds as well as with alkenes and alkynes (vide infra). They also show high reactivity towards -donors, such as alcohols, ethers, amines, amides, imides, carbodiimides, oximes, hydrazones, sulfides, sulfoxides, halides, and phosphines. However, their reactivity toivards cf-donors is understandably much lower. 

There has been much interest in the reactivity of nitronium salts, for example, toward amides in acetonitrile,the oxidation of alkanes in acetonitrile (via a carbenium ion intermediate),and toward organic sulfides, phosphines, arsines, and stibines. Reaction with diaryl, aryl alkyl, and dialkyl sulfides give sulfoxides, but a few percent of the ring C-nitro products were found for diphenyl sulfide. This is a result of the equilibrium between nitrito onium ions ] X-ONO and nitronium ions This is the first demonstration of the ambident reactivity... 

Both nitronium and nitrosonium salts are effective initiators but with quite different results. Thus, propene and nitronium fluoroborate react to produce the secondary a-nitrocarbenium ion which undergoes Ritter reaction with acetonitrile to yield amide (118). Under similar conditions, nitrosonium fluoroborate leads to heterocyclic products. Intramolecular reaction of the nitroso and nitrilium groups, followed by prototropic shifts, affords the iV-hydroxy imidazolium salt (119). This may be either neutralized to produce the iV-oxide or reduced to the imidazole (120 Scheme SS). 

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