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The Stabilization of Lithiated Organic Compounds by Water as a Ligand – Synthesis of a New Lithium–Imidazole Complex and Regioselective Reactions with Selected Electrophiles
Author(s) -
Atzrodt Jens,
Beckert Rainer,
Bräuer Michael,
Nordhoff Karsten,
Anders Ernst,
Görls Helmar
Publication year - 1998
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/(sici)1099-0690(199811)1998:11<2557::aid-ejoc2557>3.0.co;2-z
Subject(s) - chemistry , deprotonation , regioselectivity , electrophile , imidazole , medicinal chemistry , molecule , amide , stereochemistry , crystallography , organic chemistry , ion , catalysis
The deprotonation of the 4 H ‐imidazoles 1 by lithium hydride yields the lithiated derivatives 2 which contain a stable delocalized anion. Surprisingly, the X‐ray crystal structure analysis of 2a reveals one molecule of water in the first complexation sphere of the lithium cation. This result is in good agreement with semiempirical calculations (PM3) which predict an increase in stability on substitution of ether ligands by water molecules. The deprotonation of 1 is accompanied by a change of colour from orange to purple because of the polymethinic character of the resulting anion. Alkylation, as well as acylation, of 2 leads to the exocyclic substituted derivatives 3 and 5 . The NMR spectra of 3 and 5 and the semiempirical calculations suggest the existence of two rotamers due to the low rotation barrier of the exocyclic C–N bond. Another type of acylation is observed when phenylacetyl chloride is used as an acylating agent. The X‐ray crystal structure analysis of 6c reveals that a rearrangement forming an unsaturated acid amide substructure takes place.