CONFORMATIONAL AND CHIROPTICAL PROPERTIES OF N-NITROSOAZETIDINES

Optically active N-nitrosoazetidines, containing the isolated nitrosoazetidine chromophore, i.e. (2R)-1-nitroso-2-methylazetidine (2) and (4S)-1-nitroso-2,2-dibutyl-4-methylazetidine (5), are synthesized, and their H-1 NMR, CD, and UV spectra are studied. A topomerization mechanism, structural features, and chiroptical properties of the individual isomers of the parent 1-nitrosoazetidine (1) and its (2R)-2-methyl, (4R)-2,2,4-trimethyl, and (4S)-2,2-diethyl-4-methyl derivatives 2-4 are studied theoretically by means of non-empirical quantum chemical calculations. It is shown that the CD spectra of N-nitrosoazetidines can be interpreted on the basis of the two-position Z,E-equilibrium, taking into account the nonplanarity of the nitrosoazetidine chromophore. The Cotton effect sign of the n-pi* transition at 380 nm is determined by the intrinsic chirality of the chromophore and obeys a spiral rule.