A new route to construct the carbon skeleton of germacrane sesquiterpenes is described wherein the 13-membered diallylic ethers 12 and 41, prepared by intramolecular O-alkylation of the bromo alcohol and C-alkylation of the cyanohydrin ether respectively, undergo [2,3]-Wittig rearrangement to give the ten-membered carbocycles. Diastereoselectivity in [2,3]-Wittig rearrangement is discussed based on