A short and enantioselective preparation of taxol A-ring fragment

Two short preparations of the taxol A-ring fragment are described: one via organocatalyzed α-aminoxylation and the other via Sharpless asymmetric dihydroxylation (SAD). The former approach affords the A-ring fragment in 10 steps, and the latter approach involves eight steps to afford the new A-ring fragment in 91% ee, which is made enantiomerically pure through recrystallization. The new A-ring fragment bearing a bromoalkene is confirmed to be useful to form the carbocyclic eight-membered ring of a taxol model compound by palladium-catalyzed intramolecular alkenylation. The preparation of the new A-ring fragment will be beneficial for the total synthesis of taxol as well as other natural products