Chemistry of N-nitroso compounds. 3. Synthesis and conformational analysis of N-nitrosohexahydro-1,4-diazepin-5-ones
作者:Udayampalayam P. Senthilkumar、Ramasubbu Jeyaraman、Robert W. Murray、Megh Singh
DOI:10.1021/jo00048a041
日期:1992.10
A comparison of the barrier to N-X rotation in a series of compounds with various N-X=Y systems has shown that the N-nitrosamines, some of which have been found to be highly carcinogenic, exhibit the highest rotation barrier. All the other systems which, to date, have not been found to be carcinogenic have lower barriers. With a view to studying the influence of the N-nitroso group on the conformations of N-nitrosodiazepinones, several 1-nitroso-r-2,c-7-diphenylhexahydro-1,4-diazepin-5-ones 16-20 were synthesized from the corresponding r-2,c-7-diphenylhexahydro-1,4-diazepin-5-ones 11-15 and their conformations in deuterated solvents were studied. The N-nitrosodiazepinones 16-20 were found to prefer boat conformations, with some flattening at the nitroso end of the ring and with quasi-axial phenyl groups. As shown earlier, N-nitroso-r-2,c-6-diphenylpiperidines prefer partially twisted chair conformations with equatorial phenyl groups and r-2,c-6-dimethyl-N-nitrosopiperidine prefers a chair conformation with 1,3-diaxial methyl groups. The title compounds 16-20 exist in conformational equilibria involving syn and anti orientations of the coplanar nitroso group in an approximate syn-anti ratio of 60:40 (observed from H-1 NMR spectroscopic studies). The C-13 NMR spectra of these compounds show that the carbons syn to the nitroso group are shifted upfield by about 11-15 ppm compared to the precursor compounds 11-15, while the anti carbons were shifted by less than 1 ppm in either direction. It was observed that all of the syn alpha-protons are more deshielded than the anti alpha-protons while for the beta-protons the reverse is true. The N-N=O rotational barriers for these compounds could not be determined precisely since they start decomposing above 150-degrees-C in DMSO-d6 Solutions. A rough estimate of the energy barrier for the isopropyl derivative 19 shows that the barrier is at least 21.5 kcal mol-1.