Ab initio theoretical study of 3-aminopyrrolidines lithium amides as chiral ligands for butyllithium
Abstract
DFT computations on 3-N-methylamino-N-methylpyrrolidine lithium amide and its complex with methyllithium are reported. The results obtained fully support the norbornyl-like folding adopted by the pyrrolidine ring that has been inferred from experimental NMR data. The 6Li and 13C theoretical nuclear magnetic shielding constants are in reasonable agreement with the corresponding measured chemical shifts for parent compounds. The comparison between experimental and theoretical results confirms that, for the 3-aminopyrrolidines experimentally studied, there is, in solution, a delicate balance between steric repulsions and aggregation forces. On the other hand, the model systems considered in this preliminary study are able to account for the energy scale of most of the different possible intermolecular interactions but not for the driving forces at work in the aldehyde-lithium amide condensation reaction.