The Stabilization of Lithiated Organic Compounds by Water as a Ligand – Synthesis of a New Lithium–Imidazole Complex and Regioselective Reactions with Selected Electrophiles

Abstract

The deprotonation of the 4H‐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, of2 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.

Quantum-chemical Research of the Mechanism of Reaction of an Acylating Butylmethylamine by Propionyl Chloride in the Presence of Lithium Hydride

“…Квантово-химические расчёты были проведены для реакции (1), как ключевой в первом пути синтеза и для реакции (5).…”

“…В результате ранее проведенных работ, как собственных [3], так и других авторов [4][5][6], была показана возможность применения гидрида лития в качестве акцептора хлороводорода в реакции ацилирования по атому азота хлорангидридами карбоновых кислот. Данный способ получения амидов лишён представленных выше недостатков.…”