New Cascade Syntheses of Nitronyl Nitroxides and a New Synthetic Approach to Imino Nitroxides

摘要: Suspensions of MxOy (MnO2, Co2O3, Ni2O3) in protic solvents (MeOH, EtOH) have been found to be suitable systems for use a cascade transformation 4,4,5,5-tetramethyl-2-[2-(trimethylsilyl)ethynyl]imidazolidine-1,3-diol (1a) into 2-ethynyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide (3). In MnO2/MeOH, the products further 3, (Z)- and (E)-2-(2-methoxyvinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxides, were obtained by regiospecific addition MeOH triple bond 3. reaction MnO2/MeOH+H2O (1:1), Z isomer was sole product. A multistep one-pot 1 4,4,5,5-tetramethyl-2-[2-oxo-1-(4,4,5,5-tetramethylimidazolidin-2-ylidene)ethyl]-4,5-dihydro-1H-imidazole-1-oxyl occurred MnO2/EtOH. For (E)-2-[2-(diethylamino)vinyl]-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide, it shown that MnO2/secondary amine system provided 1a gave (E)-aminovinyl-substituted nitronyl nitroxide as combined MnO2/ROH/K2CO3 (R = Me, Et), imidazolidine-1,3-diol transformed (E)-2-(2-ethoxyvinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl acetals 2-(2,2-dimethoxyethyl)- 2-(2,2-diethoxyethyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide. MnO2/MeNO2 we transformations different 2-substituted 4,4,5,5-tetramethylimidazolidine-1,3-diols C≡C–SiMe3, aryl, hetaryl, alkyl) or nitroxides corresponding imino (13 products); this is new method preparation allowed us synthesize first α-acetylenyl-substituted nitroxides. The majority paramagnetic compounds, including derivatives 1a, perfect crystals, their structures determined X-ray structure analysis (14 solved structures). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)