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Solvent‐Dependent Mixed Complex Formation—NMR Studies and Asymmetric Addition Reactions of Lithioacetonitrile to Benzaldehyde Mediated by Chiral Lithium Amides
Author(s) -
Sott Richard,
Granander Johan,
Hilmersson Göran
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020503)8:9<2081::aid-chem2081>3.0.co;2-q
Subject(s) - benzaldehyde , lithium (medication) , chemistry , solvent , solvent effects , isotopes of lithium , asymmetric induction , computational chemistry , organic chemistry , enantioselective synthesis , catalysis , ion , ion exchange , medicine , endocrinology
Lithioacetonitrile and a chiral lithium amide with an internally coordinating methoxy group form mixed dimers in diethyl ether (DEE) and in tetrahydrofuran (THF) according to NMR studies. Based on the observed 6 Li, 1 H heteronuclear Overhauser effects, in THF lithioacetonitrile is present in a mixed complex with the chiral lithium amide, and this complex has a central N‐Li‐N‐Li core. In DEE, on the other hand, the acetonitrile anion bridges two lithiums of the dimer to form a central six‐membered Li‐N‐C‐C‐Li‐N ring. Gauge individual atomic orbital DFT calculations of the 13 C NMR chemical shifts of the DEE‐ and THF‐solvated mixed dimers show good agreement with those obtained experimentally. Lithioacetonitrile complexed to the chiral lithium amide has been employed in asymmetric addition to benzaldehyde in both DEE and THF. In THF the product, ( S )‐3‐phenyl‐3‐hydroxy propionitrile, is formed in 55 % ee and in DEE the R enantiomer is formed in 45 % ee. This change in stereoselectivity between solutions in DEE and THF was found to be general among a number of different chiral lithium amides, all with an internal chelating methoxy group.