Protecting-Group-Free Total Synthesis of (E)- and (Z)-Alstoscholarine

Stereoselective Total Synthesis of Eburnane-Type Alkaloids Enabled by Conformation-Directed Cyclization and Rearrangement

Controlling the cis C20/C21 relative stereochemistry remains an unsolved issue in the synthesis of eburnane-type indole alkaloids. Provided herein is a simple solution to this problem by developing a unified and diastereoselective synthesis of four representative members of this class of natural products, namely, eburnamonine, larutensine, terengganensine B, and melokhanine E. The synthesis features the following key steps: a) an α-iminol rearrangement transforming the 3-hydroxyindolenine into spiroindolin-3-one, b) a highly diastereoselective conformation-directed cyclization leading to the melokhanine skeleton with the desired C20/C21 cis stereochemistry, and c) either an aza-pinacol or an unprecedented α-aminoketone rearrangement converting spiroindolinone back into the indole skeleton.

Ruthenium-Catalyzed Metathesis Cascade Reactions in Natural Products Synthesis

In this account, we provide a brief summary of recent developments in ruthenium-catalyzed metathesis cascade reactions towards the total synthesis of natural products. We also highlight recent progress from our own laboratory regarding the synthesis of securinega alkaloids and humulanolides, which has resulted in the development of novel ruthenium-catalyzed metathesis cascade reactions. Inspired and guided by the pioneering and elegant research conducted in this area, we developed a regio-controlled relay dienyne metathesis cascade reaction and a cyclobutene-promoted RCM/ROM/RCM cascade reaction for the synthesis of securinega alkaloids and humulanolides, respectively.

Enantioselective Total Synthesis of (-)-Terengganensine A

A seven-step enantioselective total synthesis of (-)-terengganensine A, a complex heptacyclic monoterpene indole alkaloid, was accomplished. Key steps included: a) Noyori's catalytic enantioselective transfer hydrogenation of the iminium salt to set up the absolute configuration at the C21 position; b) a highly diastereoselective C7 benzoyloxylation with dibenzoyl peroxide under mild conditions; and c) an integrated one-pot oxidative cleavage of cyclopentene/triple cyclization/hydrolysis sequence for the construction of the dioxa azaadamantane motif with complete control of four newly generated stereocenters.

Phosphoric acid catalyzed desymmetrization of bicyclic bislactones bearing an all-carbon stereogenic center: total syntheses of (-)-rhazinilam and (-)-leucomidine B

In the presence of a catalytic amount of an imidodiphosphoric acid, enantioselective desymmetrization of bicyclic bislactones by reaction with alcohols took place smoothly to afford enantiomerically enriched monoacids having an all-carbon stereogenic center. Concise catalytic enantioselective syntheses of both (-)-rhazinilam and (-)-leucomidine B were subsequently developed using (S)-methyl 4-ethyl-4-formylpimelate monoacid as a common starting material.