A NMR and Theoretical Study of the Aggregates between Alkyllithium and Chiral Lithium Amides:  Control of the Topology through a Single Asymmetric Center

The complexes between methyllithium and chiral 3-aminopyrrolidine (3-AP) lithium amides bearing a second asymmetric center on their lateral amino group were studied using multinuclear (1H, 6Li, 13C, 15N) low-temperature NMR spectroscopies in tetrahydrofuran-d 8. The results indicate that lithium che...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2002-12, Vol.124 (51), p.15267-15279
Main Authors: Corruble, Aline, Davoust, Daniel, Desjardins, Stéphanie, Fressigné, Catherine, Giessner-Prettre, Claude, Harrison-Marchand, Anne, Houte, Henri, Lasne, Marie-Claire, Maddaluno, Jacques, Oulyadi, Hassan, Valnot, Jean-Yves
Format: Article
Language:English
Subjects:
Chemical Sciences
Chemistry
Exact sciences and technology
General and physical chemistry
Solution properties
Solutions
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Summary:The complexes between methyllithium and chiral 3-aminopyrrolidine (3-AP) lithium amides bearing a second asymmetric center on their lateral amino group were studied using multinuclear (1H, 6Li, 13C, 15N) low-temperature NMR spectroscopies in tetrahydrofuran-d 8. The results indicate that lithium chelation forces the pyrrolidine ring of the 3-AP to adopt a norbornyl-like conformation and that robust 1:1 noncovalent complexes between methyllithium and 3-AP lithium amides form in the medium. A set of 1H-1H and 1H-6Li NMR cross-coupling correlations shows that the binding of methyllithium can take place along the “exo” or the “endo” face of this puckered structure, depending on the relative configuration of the lateral chiral group. This aggregation step renders the nitrogen of the 3-amino group chiral, the “exo” and “endo” topologies corresponding to the (S) and (R) configurations, respectively, of this atom. Density functional theory calculations show that the “exo” and “endo” arrangements are, for both diastereomers, almost isoenergetic even when solvent is taken into account. This result suggests that the formation of the mixed aggregates is under strict kinetic control. A relationship between the topology of these complexes and the sense of induction in the enantioselective alkylation of aromatic aldehydes by alkyllithiums is proposed.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja016945d