Nitroethylene reaction with benzene

As seen in the gitonic and vicinal systems, ammonium and related cationic centers may be components of superelectrophiles and reactive dications having the 1,3-dicationic structure. Several types of superelectrophilic aza-carbo dications have been studied in which protonated nitro groups are involved. For example, it was found that nitroethylene reacts with benzene in the presence of 10 equivalents of CF3SO3H to give deoxybenzoin oxime in 96% yield (eq 58).71 Since the reaction does not occur with only one equivalent of CF3SO3H, the formation of the /V./V -dihydroxy iminium-methyl dication 197 was proposed. In spectroscopic studies, the stable dication (199) can be directly observed by H and 13C NMR spectroscopy from solutions of l-nitro-2-methyl-l-propene (198) in CF3SO3H (eq 59). 

Reaction of a 5-alkoxy-4-methyloxazole with nitroethylene in benzene at -4°, followed by acid hydrolysis, leads to the 3-nitropyrrole 3 (57%).2 1-Nitropropene similarly gave 2-acetyl-4-methyl-3-nitropyrrole (4).3 The initial Diels-Alder adduct under acidic conditions is transformed as in Scheme 2. 

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