Cocondensation Reactions of Five‐Membered Heterocycles with Lithium Atoms at 77 K

Abstract

Lithium atoms were cocondensed with eight aromatic five‐membered heterocycles in the presence of THF at 77 K. In the case of the oxygen‐ and sulfur‐containing heterocycles (furans and thiophenes), the reaction resulted in C−H bond activation and led to the corresponding aryllithium compound. The other heterocycles (pyrroles) failed to react with lithium atoms in the presence of THF. A special case was found when oxazole was reacted under these cocondensation conditions; here a dilithiated product was obtained. DFT (B3LYP/6‐31G**) calculations were carried out in order to interpret the pathways of the reactions and the possible intermediates. For all the reactions π‐ and σ‐complexes between lithium clusters and the heterocycles were found as stable intermediates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Cocondensation reactions of heterocyclic aromatic compounds with lithium, calcium and magnesium atoms at 77K

“…Previous research in this area showed that five-membered heterocycles react with lithium atoms in the presence of THF under cocondensation conditions [8]. The isolated products were identified as lithiated aromatic compounds.…”

“…No reaction [8] No reaction (15), this Ca-O interaction is lost (d CaO : 326.2 pm). This is due to the coordination number 6 at the calcium centre; now the intramolecular donor furyl cannot compete against the solvent molecules.…”

“…The work has been expanded to +I substituted (CMe 3 , SiMe 3 , o-and m-xylene) and donor substituted (OMe, NMe 2 , SMe) benzene derivatives [7] as well as five-membered heterocycles [8] and nitrogen-containing heterocycles [9]. In the case of anisole a selective C-H bond activation was found to occur in the absence of THF as well; its reaction mechanism was calculated in detail in a recent DFT study [10].…”

“…Previous reports have shown successful cocondensation [8] reactions of lithium atoms and five-membered heterocycles. When the heterocycle used was furan (1) or thiophene (2), the reaction led to a monolithiated species.…”

“…4-Picoline (8) was reacted with magnesium, calcium and lithium atoms and for all the cases the product was identified as a nonmetallated compound. Also a C-H activation took place, but surprisingly, an aryl C-H bond was not activated.…”