Controllable Cycloadditions between 2<i>H</i>-(Thio)pyran-2-(thi)ones and Strained Alkynes: A Click-and-Release Strategy for COS/H₂S Generation.

In this work, we carried out computational studies to predict the cycloaddition efficiency of strained alkynes with 2<i>H</i>-pyran-2-one and its three sulfur-containing analogues: 2<i>H</i>-pyran-2-thione, 2<i>H</i>-thiopyran-2-one, and 2<i>H</i>-thiopyran-2-thione. It was predicted that the decreased aromaticity of the substrate would yield higher reactivity. Experimental studies confirmed the calculation results, and 2<i>H</i>-pyan-2-thiones were found to be the most reactive substrates. This reaction proceeded effectively in aqueous buffers and in cellular environments. It also produced COS as the byproduct, which could be converted into hydrogen sulfide (H₂S) in the presence of carbonate anhydrase. This click-and-release approach may serve as a unique way to deliver COS/H₂S to specific locations.