title: A NMR and theoretical study of the aggregates between alkyllithium and chiral lithium amides: control of the topology through a single asymmetric center.
abstract: 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 ((1)H, (6)Li, (13)C, (15)N) 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 (1)H-(1)H and (1)H-(6)Li 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.
authors.affiliation: Laboratoire des Fonctions Azotées & Oxygénées Complexes de l'IRCOF, UMR 6014 CNRS, Université de Rouen, 76821 Mont St Aignan Cédex, France.
authors.forename: Aline
authors.initials: A
authors.lastname: Corruble
authors.forename: Daniel
authors.initials: D
authors.lastname: Davoust
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Desjardins
authors.forename: Catherine
authors.initials: C
authors.lastname: Fressigné
authors.forename: Claude
authors.initials: C
authors.lastname: Giessner-Prettre
authors.forename: Anne
authors.initials: A
authors.lastname: Harrison-Marchand
authors.forename: Henri
authors.initials: H
authors.lastname: Houte
authors.forename: Marie-Claire
authors.initials: MC
authors.lastname: Lasne
authors.forename: Jacques
authors.initials: J
authors.lastname: Maddaluno
authors.forename: Hassan
authors.initials: H
authors.lastname: Oulyadi
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Valnot