Synthesis of Densely Substituted Sulfonylfurans and Dihydrofurans via Cascade Reactions of α‑Functionalized Nitroalkenes with β‑Ketosulfones

The reaction of β-ketosulfones
with different α-functionalized
nitroalkenes affords diversely substituted sulfonylfurans and dihydrofurans.
Furthermore, β-ketosulfones react with α-bromonitroalkenes
and α-hydrazinonitroalkenes via a cascade Michael addition-cyclization
protocol to afford nitrodihydrofurans and hydrazinodihydrofurans,
respectively, bearing a key sulfonyl group, in excellent yields with
a broad substrate scope. Application of these products has been demonstrated
by the synthesis of pyrroles and pyrazoles in good yields. The reaction
of β-ketosulfones with nitroallylic acetates yields tetrasubstituted
sulfonyl furans through a cascade SN2′-intramolecular
Michael reaction, followed by aromatization. The gram-scale synthesis
of a representative example of sulfonylfurans was carried out to demonstrate
the synthetic efficiency of the methodology.