Tokyo, Hongo, Bunkyo-ku, (3-Nitrostyrenes are diprotonated on the nitro group to yield N,N-dihydroxyiminium-benzyl dications in trifluoromethanesulfonic acid. These dications comprise a new class of reagents that can react with benzene. The reaction is dependent on the substituent (H or alkyl group) at the K position of nitrostyrene: Bnitrostyrene yields diphenylacetophenoneoxime, and f3-methyl-B-nitrostyrene yields acetophenoneoxime and triphenylmethane. An essentially common mechanism is suggested to be involved in both reactions. These reactions are novel examples of acidcatalyzed reactions of nitro olefins. Diprotonation of a nitro group was recognized for the first time in the case of nitronaphthalenes in a strongly acidic medium.' We also reported the diprotonation of &nitrostyrenes in a strong acid2: f3-nitrostyrenes (1, 2) form N,N-dihydroxyiminium-benzyl dications (3 and 4, respectively) in trifluoromethanesulfonic acid (TFSA). These findings encouraged us to clarify the formation and reactivities of H N02 2 H+ ) #H-&OH H & N02 2 H+ CH3 2 diprotonated species of nitro olefins, since the diprotonation of nitroarenes to be a restricted phenomenon at the present stage. In this paper, we will seems describe the formation and the reactions of N,N-dihydroxyiminium-benzyl dications. This confirms the discrete existence of these dications evaluated by means of cryoscopic, spectroscopic and 'SO-isotope incorporation experiments. These dications are considered to be novel reactive electrophiles which comprise a new class of reagents that can react with non-activated benzenes. Another aim of the study was to establish the acid-catalyzed reaction of nitro olefins. Though nitro olefins 297