J. Philipp Wagner

Thermolysis of thiirane oxide leads to production of highly reactive sulfur monoxide. The liberated SO can in turn be trapped with a diene scavenger forming dihydrothiophene oxide. Since the intermediate diatomic possesses a triplet ground state, the SO transfer can proceed on two spin‐state surfaces. Here, we study the competition between singlet concerted and stepwise triplet diradical mechanisms utilizing the M06‐2X density functional as well as CCSD(T) and MRCI+Q wavefunction theories. We find that the decomposition of thiirane oxide prefers to pass through a triplet diradical intermediate that becomes accessible from a nearby minimum energy crossing point (MECP). Hence, the thermolysis of thiirane oxide is expected to predominantly release triplet ground state sulfur monoxide in agreement with previous experimental reports. The addition of 3 SO to 1,3‐butadiene initially generates an allylic diradical, that ring‐closes to a thiirane oxide through another MECP, and a subsequent rearrangement gives access to the final product.