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%. The favorability
of an SNAr-like mechanism for the cyclization was supported
by DFT calculations. The applicability of the developed procedure
to modification of natural compounds was demonstrated by preparation
of a deoxycholic acid derivative.
A convenient approach to assemble 1,2,3-triazole-fused 4H-3,1-benzoxazines has been developed. Diverse alcohol-tethered 5-iodotriazoles, readily accessible by a modified protocol for the Cu-catalyzed (3+2)-cycloaddition, were utilized as precursors of the target fused heterocycles. The intramolecular C–O coupling proceeded efficiently under base-mediated transition-metal-free conditions, furnishing cyclization products in yields up to 96%. Suppression of the competing reductive cleavage of the C–I bond was achieved by the use of Na2CO3 in acetonitrile at 100 °C. This practical and cost-effective procedure features a broad substrate scope and valuable functional group tolerance.
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