Expanding Isothiazole Chemical Space: Synthesis and Derivatization of [ <i>c</i> ]-Fused Saturated Rings

This work presents the first synthetic route toward 3-unsubstituted [<i>c</i>]-fused isothiazoles in three steps from commercially available saturated ketones, exemplified for more than 15 hitherto undescribed [<i>c</i>]-fused isothiazoles. Unlike prior methods relying on prefunctionalized scaffolds, the unsubstituted core enables versatile late-stage functionalization at the 3-position, demonstrated by six different functionalization pathways.