Trimethylenemethane (TMM) is a reactive intermediate whose main application in organic synthesis is the production of cyclic compounds. Application of TMM in synthesis of carbon cycles and heterocycles has been described in the scientific literature, but its reactions with SO2 to obtain sulfur heterocycles are still unknown.1 Sultines are cyclic sulfinate esters that have so far been little studied in organic synthesis. However, sultines are potentially applicable as versatile building blocks for obtaining biologically active molecules, as they undergo ring-opening, alkylation, reduction and oxidation reactions, giving access to various classes of useful substances.2,3 The aim of the work is to investigate the reaction of TMM with SO2, obtaining cyclization products - sultines, and to consider the possibilities of their derivation. The generally accepted methods of organic synthesis, separation, purification and characterization of substances were used in the development of the work, as described in the previous works of our scientific group.4 A range of different sultines were successfully obtained, the structure of which was confirmed by X-ray diffraction. A new synthetic method was optimized by determining the best palladium source, ligand, temperature and solvent and achieving reaction yields of up to 83%. The resulting sultins were also derivatized, elucidating an interesting and hitherto unknown reactivity for such products. References. 1. Yamago, S.; Nakamura, E. [3+2] Cycloaddition of Trimethylenemethane and its Synthetic Equivalents. In Organic Reactions; Wiley: Hoboken, NJ, USA, 2002; pp. 1–217. 2. Zhu, Z.; Deng, Z.; Ouyang, X.; Shu, C. Synlett 2023, 34 (17), 1943–1947. 3. Zhang, Y.; Li, H.; Yang, X.; Zhou, P.; Shu, C. Chem. Commun. 2023, 59(42), 6272–6285. 4. Gulbe K.; Turk M. J. Org. Chem. 2020, 85, (8), 5660–5669.