To explore the chemical space of the original conversion reaction of nitrile oxide into isocyanate in greater detail, we first screened the possible pathways at B3LYP-D3(BJ)/6-31G level of theory in the gas phase. The results of this screening are outlined in Figure . We explored two main pathways, proceeding through two possible intermediates, denoted as Intermediate #1 and #2. Intermediate #1 resembles the initially assumed mechanism (see initial post), in which the whole nitrile oxide (C ---N + -O -) group of the reactant and a single S--O bond of the SO 2 participate in [3+2]-cycloaddition to form a five-membered ring. In the Intermediate #2, a similar process occurs with the whole SO 2 and C ---N + part of the C ---N + -O --group.