Trimethylenemethane (TMM) is a known reaction intermediate, which can be represented as 4 carbon conjugated structure of diradical or zwitterion.1 TMM has been shown to react with carbonyl-, iminyl-, cyano- groups and C-C double or triple bonds to form cyclic compounds. Specifically, its reaction with CO2 has been previously reported.2Herein, we unveil novel TMM reactivity towards SO2. TMM is generated in situ from easily obtainable methylenecyclopropanes 1 through palladium catalysis, followed by the cycloaddition to SO2, which yields γ-sultines 2.Investigation of γ-sultine 2 reactivity has shown that these products are stable, but seemingly can regenerate TMM through palladium catalysis, and thus react with nucleophiles under milder conditions than described in literature.3 Furthermore, γ-sultines 2 can be opened by carbon nucleophiles generating sulfoxides 4.Acknowledgements:E. Š. thanks RTU Master student grant ZM-2024/19 for financial support.ReferencesYamago, S.; Nakamura, E. [3+2] Cycloaddition of Trimethylenemethane and Its Synthetic Equivalents. In Organic Reactions; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2002; pp 1–217. Chen, K.; Jiang, M.; Zhang, Z.; Wei, Y.; Shi, M. European J. Org. Chem. 2011, No. 35, 7189–7193.Siriwardana, A. I.; Kamada, M.; Nakamura, I.; Yamamoto, Y. J. Org. Chem.2005, 70 (15), 5932–5937.: