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.