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First Direct Evidence of an ortho ‐Lithiated Aryloxetane: Solid and Solution Structure, and Dynamics
Author(s) -
Perna Filippo M.,
Falcicchio Aurelia,
Salomone Antonio,
Milet Anne,
Rizzi Rosanna,
Hamdoun Ghanem,
BarozzinoConsiglio Gabriella,
Stalke Dietmar,
Oulyadi Hassan,
Capriati Vito
Publication year - 2019
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201900949
Subject(s) - chemistry , crystallography , dilithium , lithium (medication) , synthon , crystal structure , ligand (biochemistry) , tetramethylethylenediamine , denticity , lithium atom , cryptand , oxetane , stereochemistry , organic chemistry , medicine , ion , biochemistry , receptor , ionization , deprotonation , endocrinology
Oxetanes are key synthons for asymmetric synthesis and also effective in directing ortho ‐lithiation. This work first reports the solution and the solid‐state structure of an ortho ‐lithiated aryloxetane ( 1‐Li ) in the presence/absence of a bidentate ligand such as N , N , N′ , N′ ‐tetramethylethylenediamine (TMEDA). Single crystal X‐ray diffraction analysis of 1‐Li revealed a singular crystallographic structure in which the asymmetric unit comprises a core where the lithium atom is coordinated to the nitrogen atom of half a molecule of TMEDA and intramolecularly stabilised by the oxetane ring oxygen. This aggregation state is unprecedented in ortho ‐lithiated arenes. Variable temperatures multinuclear magnetic resonance ( 1 H, 7 Li, 13 C) mono‐ and two‐dimensional NMR studies and DFT computations supported the coexistence in solution of three chelated bridged dimeric aggregates, in slow equilibration at 180 K. The major isomer is an heterochiral aggregate on the basis of 1 H, 7 Li‐HOESY and 1 H, 1 H‐NOESY experiments. Conclusions were supported by the preparation of enantiomerically enriched ( S )‐ 1‐Li . The privileged formation of homochiral aggregates from racemic mixtures may also have implications for the development of chiral resolution processes.