SYNTHESIS OF MEDIUM RING ETHERS .2. SYNTHESIS OF THE FULLY SATURATED CARBON SKELETON OF LAURENCIA NON-TERPENOID ETHER METABOLITES CONTAINING 7-MEMBERED, 8-MEMBERED AND 9-MEMBERED RINGS

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.