Metallation of Ketazines: Reaction of Tetralone Azine with Methyllithium

The reaction of tetralone azine with methyllithium in tetrahydrofuran releases 1 mol of CH₄ and yields the lithium salt of enamine I, which crystallizes as a dimer in which lithium atoms bridge the sp³- and sp²-hybridized nitrogen atoms of two ligands, forming a six-membered LiNNLiNN metallacycle (CCDC no. 2426300). Analysis of the electron density topology using the noncovalent interaction index and source function revealed that each lithium atom in complex I interacts with the NNCC fragment of the ligand. Charge distribution analysis in the ligand anion showed that position C(2) is the most favorable site for electrophilic attack. DFT calculations demonstrated that phosphorylation of deprotonated tetralone azine with PCl₃ is thermodynamically more favorable by 12.6 kcal/mol than phosphorylation at the nitrogen atom.