Synthetic studies towards pentacyclic quassinoids: Total synthesis of (-)-samaderine Y from (S)-(+)-carvone

In this thesis, a review concerning pentacyclic quassinoid total syntheses from 1990 to 2005 and structure activity relationship is presented.; Synthetic studies towards pentacyclic quassinoids, namely (-)-samaderine E and (-)-samaderine Y from (S)-(+)-carvone are described. Total synthesis of (-)samaderine Y was accomplished in 21 steps with 1.1% overall yield in which the synthesis was based on a C→CE→ABCE→ABCDE ring annulation sequence. The crucial points included: (1) a regioselective allylic oxidation to functionalize C ring; (2) a stereoselective epoxymethano bridge formation; (3) an intramolecular Diels-Alder reaction resulting in the construction of AB ring; (4) an intramolecular aldol reaction for the construction of D ring; (5) a regioselective allylic oxidation and an alpha-keto acetoxylation to functionalize the A ring.