Stereoselective Reduction of Bicyclic Ketals. A New, Enantioselective Synthesis of Isolaurepinnacin and Lauthisan Skeletons

A general synthetic strategy for constructing seven- and eight-membered cyclic ether derivatives is described. The important feature of this work is a highly stereoselective reduction of bicyclic ketals, i.e., cis-selective reduction with triethylsilane/TiCl₄and trans-selective reduction with diisobutylaluminum hydride (DIBAL). The procedure completed a new and efficient synthesis of isolaurepinnacin and lauthisan skeletons in optically active forms.