On the dichotomic reactivity of lithiated styrene oxide: a computational and multinuclear magnetic resonance investigation.
A multinuclear magnetic resonance investigation, supported by density functional theory calculations, has been synergically used to investigate the configurational stability, reactivity and aggregation states of alpha-lithiated styrene oxide in THF at 173 K. NMR studies on alpha-lithiated [alpha,beta-(13)C(2)]styrene oxide (also in an enantiomerically enriched form) proved that in THF this oxiranyllithium is mainly present as a solvated monomeric species in equilibrium with a complex mixture of stereoisomeric dimeric aggregates, as well as with bridged and tetrameric aggregates. The fact that some C(alpha)-Li bonds are partially broken in some stereoisomers reduces their symmetry and complicates the NMR spectra: two diastereoisomers each having a pair of diastereotopic carbon atoms slowly inverting at the lithium atom in absence of tetramethylethylenediamine (TMEDA) have been detected. A ((13)C,(7)Li)-HMQC experiment to correlate (7)Li and (13)C resonances of the various aggregates has been performed for the first time. From natural bond analysis, the monomeric aggregate was proven to have a lower carbenoid character with respect to bridged O-coordinated dimeric aggregates. The employment of suitable experimental conditions in terms of concentration, temperature and the presence or not of TMEDA are crucial to mitigate at the best the "carbene-like" reactivity of lithiated styrene oxide toward intermolecular C-Li insertions, eliminative dimerisation reactions and ring-opening reactions. A two-step mechanism for the deprotonation of styrene oxide by sBuLi in THF has been proposed and discussed as well as competitive side reactions.
Capriati
Vito
V
Dipartimento Farmaco-Chimico, Università di Bari, Consorzio Interuniversitario Nazionale Metodologie e Processi Innovativi di Sintesi C.I.N.M.P.I.S. Via E. Orabona 4, 70125 Bari (Italy), Fax: (+39) 080-5442231.
Florio
Saverio
S
Dipartimento Farmaco-Chimico, Università di Bari, Consorzio Interuniversitario Nazionale Metodologie e Processi Innovativi di Sintesi C.I.N.M.P.I.S. Via E. Orabona 4, 70125 Bari (Italy), Fax: (+39) 080-5442231.
Perna
Filippo Maria
FM
Dipartimento Farmaco-Chimico, Università di Bari, Consorzio Interuniversitario Nazionale Metodologie e Processi Innovativi di Sintesi C.I.N.M.P.I.S. Via E. Orabona 4, 70125 Bari (Italy), Fax: (+39) 080-5442231.
Salomone
Antonio
A
Dipartimento Farmaco-Chimico, Università di Bari, Consorzio Interuniversitario Nazionale Metodologie e Processi Innovativi di Sintesi C.I.N.M.P.I.S. Via E. Orabona 4, 70125 Bari (Italy), Fax: (+39) 080-5442231.
Abbotto
Alessandro
A
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 53, 20125 Milano (Italy).
Amedjkouh
Mohamed
M
Department of Chemistry, University of Gothenburg, 412 96, Göteborg (Sweden).
Nilsson Lill
Sten O
SO
Department of Chemistry, University of Gothenburg, 412 96, Göteborg (Sweden).
D004852:Epoxy Compounds / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure; D013237:Stereoisomerism
D004852:Epoxy Compounds; C030011:carbene; D008094:Lithium; C013690:styrene oxide; D008697:Methane