Thermolysis of 3,3,5,5‐Tetramethyl‐1,2,4‐trithiolane 1‐Oxide: First Matrix Isolation of the HOSS · Radical

Flash vacuum pyrolysis of 3,3,5,5‐tetramethyl‐1,2,4‐trithiolane 1‐oxide performed at 700 °C yields the 1‐oxatrisulfan‐3‐yl radical (HOSS · ) along with disulfur monoxide (S 2 O) and diisopropyl sulfide, which were isolated in argon matrices at 10 K. Upon irradiation with UV light, the 1‐oxatrisulfan‐3‐yl radical undergoes isomerization to the 1‐oxatrisulfan‐1‐yl radical (HSSO · ). Both radicals were identified by comparison of their computed and experimental IR and UV/Vis spectra. In addition, density functional theory (DFT) computations offer a plausible explanation of the most likely reaction mechanism, suggesting that the initial step is a 1,3‐H shift with simultaneous ring opening. A 1‐oxatrisulfane derivative formed thereby undergoes fragmentations via a radical and a competitive concerted pathway leading to the observed final products. The same mechanism also governs the thermal fragmentation of di‐ tert ‐butyl disulfide S ‐oxide. Its pyrolysis at 700 °C affords an analogous set of products, including the 1‐oxatrisulfan‐3‐yl radical (HOSS · ) as the key intermediate.