Total Synthesis of Principinol B

We have accomplished the first and asymmetric total synthesis of principinol B, a grayanoid possessing an oxabicyclo3.2.1 architecture. A functionalized 5/7/6/5 tetracyclic intermediate was assembled in a convergent manner by a diastereoselective intermolecular aldol reaction and subsequent carbonyl-olefin metathesis of two enantiomerically enriched fragments. The oxabicyclo3.2.1 architecture containing a 6,10-ether bridge was constructed by the Williamson ether synthesis.