Synthesis of sulfone analog of oseltamivir precursor

We describe here the synthesis of a sulfone analog of an oseltamivir precursor. The synthesis comprises cyclization of two advanced building blocks via one-pot Michael addition and Horner–Wadsworth–Emmons reaction. The first building block was synthesized by an organocatalytic Michael addition of pentyloxyacetaldehyde to a nitroalkene. The second, alkenylsulfone, building block was prepared by oxidation followed by a Mannich type reaction. The cyclization was accomplished under microwave irradiation.