Efficient formal synthesis of oseltamivir phosphate (Tamiflu) with inexpensive D-ribose as the starting material.

An efficient formal synthesis of oseltamivir phosphate (Tamiflu) has been achieved in 12 steps with use of the inexpensive and highly abundant D-ribose as the starting material. This concise alternative route does not utilize protecting groups and features the introduction of 3-pentylidene ketal as the latent 3-pentyl ether, the use of a highly efficient RCM reaction to form the Tamiflu skeleton, and selective functional group manipulations.