Thiol-Free Synthesis of Oseltamivir and Its Analogues via Organocatalytic Michael Additions of Oxyacetaldehydes to 2-Acylaminonitroalkenes

The organocatalytic addition of substituted oxyacetaldehydes to 2-acylaminonitroethenes proceeded with good to high diastereoselectivities and enantioselectivities. The resulting adducts reacted with ethyl 2-(diethoxyphosphoryl) acrylate to afford highly functionalized cyclohexenes. A thiol-free protocol for cyclization has been developed that leads to a separable mixture of two diaste-reoisomers. The unwanted diastereoisomer can be efficiently epimerized. The resulting cyclohexenes are precursors to oseltamivir and its analogues. The synthesis of the key reagent, 3-pentyloxy-aldehyde, was also improved.