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

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)