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 S2'-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.