A Synthetic Approach for Constructing the 3/6/6/5-Fused Tetracyclic Skeleton of Tenuipesine A

An efficient approach toward the 3/6/6/5-fused tetracyclic skeleton of tenuipesine A has been accomplished. The strategy featured 1)a tandem Mitsunobu and 3,3-rearrangement reaction yielding the key intermediate 7 with two adjacent all-carbon quaternary centers with high d.r.; and 2)a tandem DBDMH-mediated semipinacol rearrangement via a 1,2-oxygen migration of an allylic hemiketal to construct the highly substituted tetrahydropyran ring.