6-Exo-dig cyclization/dearomatization cascade towards N-O fused spiro polyheterocycles

Herein, we present a metal-free cascade cyclization of alkyne-tethered N-alkoxybenzamides for the construction of structurally novel polyheterocycles. By using a hypervalent iodine(iii) reagent, diverse N-O fused spiro polyheterocycles are generated in good to high yields via a 6-exo-dig cyclization/dearomatization process. This approach features ambient reaction temperature, short reaction times, broad substrate scope and easy handling procedures. Importantly, preliminary antifungal activity studies suggest that N-O fused spiro polyheterocycles display good activities towards crop and forest pathogenic fungi, one of which shows 93.3% antifungal activity towards C. chrysosperma, which is much better than the positive control. © 2023 The Royal Society of Chemistry.