Medium Ring Ethers by Ring Expansion-Ring Contraction: Synthesis of Lauthisan.
A new general method for the construction of medium ring ethers has been developed. This involves the ring expansion of halo-O,S-acetals followed by a Ramburg-Backlund ring contraction reaction with concomitant extrusion of the sulfur atom. This methodol. has been utilized for the synthesis of racemic cis- and trans-lauthisan (I and II resp.).