Synthesis of medium ring ethers. Part 2. Synthesis of the fully saturated carbon skeleton of Laurencia non-terpenoid ether metabolites containing seven-, eight- and nine-membered rings

Abstract

A general method for the construction of medium ring ethers is described in which a 2-substituted cycloalkanone was subjected to a Baeyer–Villiger ring expansion to the lactone, Tebbe methylenation of which afforded the enol ether which was subjected to a hydroboration–oxidation sequence to afford the 2,n-disubstituted oxacycle (n= ring size). Application of this procedure has led to efficient syntheses of the fully saturated skeletons corresponding to the naturally occurring Laurencia metabolites containing 2,n-dialkyl substituted seven-(isolaurepan), eight-(lauthisan and laurenan) and nine-membered (obtusan) ethers.