A Route to Triazole-Fused Sultams via Metal-Free Base-Mediated Cyclization of Sulfonamide-Tethered 5-Iodotriazoles

An efficient direct approach to triazole-fused sultams has been developed. The key step of the proposed strategy is base-mediated cyclization of sulfonamide-tethered 5-iodo-1,2,3-triazoles which are readily available via an improved protocol for Cu-catalyzed 1,3-dipolar cycloaddition. The annulation of the sultam fragment to the triazole ring proceeds smoothly under transition metal-free conditions in the presence of Cs2CO3 in dioxane at 100 °C and affords fused heterocycles in high yields up to 99%. A favorability of SNAr-like mechanism for the cyclization was supported by DFT calculations. An applicability of the developed procedure to modification of natural compounds was demonstrated by a preparation of a bile acid derivative.