Overall, the mild exchange of PPh3 or N2 by isocyanides represents a new method for accessing keteniminyl anions. Metallaketenimines have received surprisingly little attention in the past, with only a handful of isolated keteniminyl metal complexes reported, all involving transition metals. To the best of our knowledge, compounds 3a-3e represent the first isolated s-block metal keteniminyl complexes. Given the widespread use of alkali metal reagents in organic synthesis, the keteniminyl anions discussed here provide an intriguing alternative entry point into the versatile chemistry of ketenimines. To demonstrate the utility of keteniminyl anions in synthesis, we conducted preliminary reactivity studies. To our delight, 3a readily undergoes transmetalation to form copper complex 9 which could be isolated as an off-white solid in a good 59 % yield (Figure ). As a result of the more covalent Cu-C bond (average: 1.928 Å), the C=C bond in 9 (average: 1.278 Å) elongates relative to 3a (1.222(6) Å), while the C-N bond decreases from 1.288( ) to approximately 1.247 Å. Furthermore, the 13 C{ 1 H} NMR signal of the C1 carbon atom appears slightly down-field shifted (47.7 ppm) relative to the potassium compound. The potassium salts of 3 were found to be highly reactive, easily engaging in reactions with unsaturated compounds to form highly functionalized heterocycles. For instance, reaction of 3a or 3b with phenyl ORCID: Content not peer-reviewed by License: CC BY 4.0 isothiocyanate, tolyl azide or the α,β-unsaturated ketone chalcone led to the formation of thiete 6, triazole 7 and the 4-hydropyran derivative 8 through a [2+2], [2+3] and [2+4] cycloaddition, respectively. All reactions proceeded selectively and allowed the isolation of the heterocycles in good to high yields between 67 and 87 %. The connectivity of the heterocycles could unambiguously be confirmed by XRD analysis (see the Supplementary Information for details). In contrast to these cycloadditions, the reaction of 3a with carbon dioxide occurred in 1:2 stoichiometry and afforded the cyclic anhydride 10, which could be isolated in a very good 88% yield. Albeit the mechanism to this novel heterocycle is unknown, it must proceed via the cleavage of one C=O double bond of CO2. The ease and high efficiency of these cyclization reactions clearly demonstrate the potential of the keteniminyl anions to access a wide range of cyclic scaffolds via a click chemistry-like approach. The formation of compound 10 also highlights the potential of this approach to access novel heterocycles, which have not been accessible through any other method.