Nitrogen Stereodynamics and Complexation Phenomena as Key Factors in the Deprotonative Dynamic Resolution of Alkylideneaziridines: A Spectroscopic and Computational Study

The present work is aimed at shedding
light on the origin of the
stereoselectivity observed in the reactions of chiral heterosubstituted
organolithiums, generated by lithiation of alkylideneaziridines. Factors
such as the nitrogen inversion barrier, the stereochemistry at the
nitrogen atom, the substitution pattern of the alkylideneaziridines,
and the reaction conditions are taken into consideration. The interplay
between nitrogen stereodynamics and complexation phenomena seems to
be crucial in determining the stereochemical outcome of the lithiation/trapping
sequence. The findings were rationalized by a synergistic use of NMR
experiments, run on the lithiated intermediates, alongside computational
data. It has been demonstrated that, in such systems, the stereochemistry-determining
step is the deprotonation reaction, and a model based on a deprotonative
dynamic resolution has been proposed. Such findings could find application
in dynamic systems other than aziridines.