Synthesis of Spiro- and Fused Heterocycles via (4+4) Annulation of Sulfonylphthalide with o‑Hydroxystyrenyl Derivatives

An expedient one-pot protocol for the synthesis of functionalized benzofuran containing fused and spiro-heterocycles has been accomplished by the modified Hauser–Kraus (HK) annulation of sulfonylphthalide with o-hydroxychalcones and o-hydroxynitrostyrylisoxazoles. The multicascade process involves Michael addition, Dieckmann cyclization, and a series of cyclizations, eliminations, and rearrangements to deliver the fused and spiro-heterocyclic products. An unusual transformation of fused indenofuran to naphthoquinone, the classical HK adduct, unraveled a novel pathway for the synthesis unsymmetrical naphthoquinones.