Efficient metathesis route to the B-ring of eleutherobin and other medium-sized cyclic ethers

A short and efficient RCM route is reported for the synthesis of the B-ring of eleutherobin and other medium-sized cyclic ethers from readily available 1,2,5,6-diisopropylidene-d-glucose. This strategy is successfully extended to the synthesis of a few bicyclic ethers, which may find applications in the synthesis of novel bicyclic nucleosides.