Rhodium-Catalyzed Enantioselective Intramolecular Hydroalkoxylation of Allenes and Application in the Total Synthesis of (R,R,R)-α-Tocopherol.

We report herein of a novel, enantioselective and rhodium- catalyzed cyclisation of allenyl alcohols towards chiral α-vinylic, cyclic ethers employing a rhodium/(R,R)-Me-ferrocelane catalyst. The corresponding chiral cyclic products were obtained in general high yield and enantioselectivities. The synthetic value of our obtained products was further exemplified by transformations of the allylic ether function. Furthermore, applying our newly developed method in our previously reported route towards the total synthesis of (R,R,R)-α-tocopherol, we were able to devise a significantly improved 2nd generation total synthesis with 12 steps in the longest linear sequence and an overall total yield of 24%.