Stereoselective synthesis of medium-sized cyclic ethers by sequential ring-closing metathesis and Tsuji–Trost allylation

Fully functionalized medium-sized cyclic ethers, of the type found in fused polyether natural products, have been prepared by sequential ring-closing diene metathesis, conversion of the resulting cyclic enone into an allylic enol carbonate, and Tsuji–Trost allylation using a chiral palladium complex. Very high levels of diastereocontrol, favoring the diastereomer in which there is a cis relationship between the allyl group at C-2 of the medium-ring ether and the substituent at C-7/C-8, are obtained in cases where catalyst control and substrate control are matched

A short sequence for the iterative synthesis of fused polyethers

A simple and efficient four‐step sequence for the synthesis of fused polyether arrays has been developed. Cyclic ethers are installed by sequential alkynyl ether formation, carbocupration, ring‐closing metathesis and hydroboration with acidic workup. Crucially, the alkene required for the subsequent ring formation by ring‐closing metathesis is present in the substrate but is masked in the form of a vinylic silane, which prevents competitive metathesis of the side chain. Generation of the reactive alkene from the unreactive vinylic silane is accomplished by hydroboration and subsequent acid‐mediated Peterson elimination of the intermediate hydroxysilane