In the reactivity studies, we focused on reactions of the cyanoketene anion with small interstellar molecules. While no reaction was observed with non-polar compounds such as dihydrogen or dinitrogen, 2 readily reacted with polar and protic compounds (Fig. ). Treatment of the cyanoketene anion with alcohols and thiols cleanly resulted in the protonation at the C1 carbon atom and formation of a carbon-oxygen bond at the C2 center. Using methanol, this reaction results in the formation of methylester 6, whereas hydrolysis provides access to cyanoacetate 4 and the corresponding acid 5, which are both industrially important compounds used as precursors to polymers, caffeine as well as several drug molecules. In an analogous fashion, reaction with hydrogen sulfide gives cyanothioacetate 7 and its acid 8 which are relevant, biologically active compounds. Treatment of the cyanoketene anion with ammonia led to the formation of compound 9 in an excellent 87% yield. To the best of our knowledge, this highly functionalized compound has never been reported before, but offers various sites for further transformations. 9 is presumably formed by initial formation of cyanoketene through deprotonation of NH3 by 2 followed by attack of a second molecule of 2 and subsequent reaction with another equivalent of NH3 (see Scheme S1). Besides cleanly reacting with protic reagents, the cyanoketene anion readily reacts with neutral heterocumulenes to form heterocycles. Reaction with carbon dioxide or carbon disulfide afforded the anhydrides 10 and 11 via cleavage of one of the C=O and S=O bond, respectively. These novel heterocycles feature a planar aromatic six-membered ring with C3-O1 and C6-O2 bond lengths of 1.222(2) Å indicating no significant electron-delocalization from the ring towards the oxygen atoms. The carbon bond lengths, however, are reminiscent of an aromatic ring system ranging from 1.399(3) Å to 1.427(3) Å. Compound 11 shows similar structural parameters to 10, with the sulfur atom adopting a trigonal pyramidal geometry and the oxygen atom being rotated out of the ring plane. This geometry around sulfur further leads to a small deviation from an ideal planar ring with a dihedral S-C-C-O angle of 9°.