Protonation and transformations of α-diazo-β-dicarbonyl compounds in superacids: generation of the strongest carbon-centered cationic electrophiles at the protonation of diazomalonates in Friedel–Crafts reactions
2016
Satumov, Eugeniy T. | Medvedev, Jury J. | Nilov, Denis I. | Sandzhieva, Maria A. | Boyarskaya, Irina A. | Nikolaev, Valerij A. | Vasilyev, Aleksander V.
Protonation of diazodiketones N2C(COR)2 in Brønsted superacids (TfOH, FSO3H, TfOH–SbF5) gives rise to stable and non-reactive O,O-diprotonated at carbonyl oxygens species N2C(C(OH+)R)2, which were studied by means of 1H and 13C NMR. Diazomalonates N2C(CO2Alk)2, contrary to diazodiketones, react with TfOH or HF, releasing nitrogen and producing triflates of oxymalonates TfOCH(CO2Alk)2 or fluoromalonates FCH(CO2Alk)2, respectively. Diazoketoesters N2C(COR)(CO2Alk) react in the same way only with TfOH, but not with HF. The reactions of diazomalonates with arenes ArH (benzene, toluene, xylenes) in TfOH solution yield corresponding Friedel–Crafts reaction products ArCH(CO2Alk)2. According to performed DFT calculations, trication +CH(C(OH+)OMe)2, a possible intermediate, which is derived from protonation of dimethyl diazomalonate, should be the strongest cationic carbon-centered electrophile known up to date.
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