H and 15N Dynamic Nuclear Polarization Studies of Carbazole
摘要:
N-15 NMR experiments, combined with dynamic nuclear polarization (DNP), are reported on carbazole doped with the stable free radical 1,3 bisdiphenylene-2-phenylallyl (BDPA). Doping shortens the nuclear relaxation times and provides paramagnetic centers that can be used to enhance the nuclear signal by means of DNP so that N-15 NMR experiments can be done in minutes. The factors were measured in a 1.4 T external field, using both unlabeled and 98% N-15 labeled carbazole with doping levels varying between 0.65 and 5.0 wt % BDPA. A doping level of approximately 1 wt % produced optimal results. DNP enhancement factors of 35 and 930 were obtained for H-1 and N-15, respectively making it possible to perform N-15 DNP NMR experiments at the natural abundance level.
An Efficient Synthesis of [15N]-Carbazole from [15N]-Aniline
摘要:
A reaction sequence involving ortho-lithiation of [N-15]-(tert-Butoxycarbonyl)aniline, quenching with Bu3SnCl, palladium catalyzed coupling with bromobenzene, and deprotection provides efficient access to [N-15]-2-aminobiphenyl (4). Compound 4 is converted to [N-15]-carbazole via diazotization, treatment with NaN3, and heating to promote intramolecular nitrene insertion.