A stable lithium stannenolate 7 was synthesized and isolated by the reaction of acylstannane 6 with LDA or tBu₂MeSiLi in THF. 7 was characterized by X-ray crystallography and by NMR and UV-Vis spectroscopy. Spectroscopic and structural features, in combination with DFT quantum-mechanical calculations, indicate that 7 is best described as an acyl-substituted stannyl anion, adopting the stannenolate keto tautomeric structure.