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PROTONATION OF 2-METHYL-l-NITRO- AND 2-METHYL-3-NITROINDOLIZINES S. I. Bobrovskii, E. V. Babaev, and Yu. G. Bundel' UDC 547.759

By PMR spectroscopy we showed that 2-methyl-l-nitro- and 2-methyl-3-nitroindolizines are protonated in an acidic medium at position 3, giving the corresponding 3H-indolizinium cations.

i

ii

Like the PMR spectra of alkylindoliziniums [1], the spectrum of the cation (I) in sulfuric acid contains the signal for the methylene group at d 5.63 s (2H, CH2) ppm, in addition to the resonance signals of the pyridine fragment. In solution in D2SO4 a slow decrease is observed in the integral intensity of the singlet (CHD) as a result of acid deuteroexchange. In the case of the cation (II) the C3H singlet (7.50 ppm) , which appears in H2S04,, is absent in D 2 SO 4 ; here the intensity of the C3H singlet (7.40 ppm) slowly decreases.* In trifluoroacetic acid 2-methyl-3-nitroindolizine is present in the neutral form, whereas the more basic 1-isomer is protonated almost completely. We note that the possibility of ipso-protonation in relation to the N02 group was demonstrated earlier [3] for the case of 4,6,8-trimethyl-l-nitroazulene [3]. LITERATURE CITED 1. 2. 3. M. Fraser, A. Melera, B. B. Molloy, and D. H. Reid, J. Chem. Soc , 1962, No. 9, 32883294. W. Engewald, C. Weiss, and M. Muhlstadt, Isotopenpraxis, 4, No. 8, 326-328 (1968). J. Schulze and F. A. Long, Proc. Chem. Soc , 1962, No. 11, 364-365; J. Am. Chem. Soc , 86, No. 3, 322-326 (1964). position 1 of 3-nitroindolizine was observed earlier [2].

*Acid deuteroexchange at

M. V. Lomonosov Moscow State University. Translated from Zhurnal Organicheskoi Khimii, Vol. 21, No. 3, p. 673, March, 1985. Original article submitted June 4, 1984.

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