The Construction of Polycyclic 4‐Imidazolidinone Skeletons via Formal [3 + 2] Cycloadditions

Abstract An efficient method has been developed for formal [3 + 2] cycloaddition reaction between α ‐halo hydroxamates and N ‐sulfonyl aldimines under basic conditions. This protocol enables the construction of a structurally diverse array of tricyclic benzosultam‐fused 4‐imidazolidinone derivatives in high yields. Mechanistic investigations indicated that a radical pathway is unlikely and a formal [3 + 2] cycloaddition mechanism is more plausible. Furthermore, the phenylmethoxyl group can be selectively cleaved using Mo(CO) 6 . By combining this approach with classical aza‐oxyallyl cation chemistry, we demonstrate a versatile platform for constructing complex heterocyclic frameworks with enhanced synthetic flexibility and potential for broad applications.