A Concise Total Synthesis of (±)‐Vibralactone

Disclosed is a five‐step synthesis of (±)‐vibralactone, a biologically active terpenoid natural product. A key photochemical valence isomerization of 3‐prenyl‐pyran‐2‐one produces both the all‐carbon quaternary stereocenter and the β‐lactone at an early stage. Cyclopropanation of the resulting bicyclic β‐lactone produces a strained housane structure that is converted to the natural product through a sequential ring expansion and reduction strategy. This concise and modular route to the natural product provides the shortest total synthesis of (±)‐vibralactone reported to date.     

Total Synthesis of (±)‐Corymine

The first total synthesis of the hexacyclic indole alkaloid (±)‐corymine is described. Starting from the readily available N‐protected tryptamine, the title compound was achieved in 21 steps in 3.4 % overall yield. Key steps of the synthesis include: a) the addition of a malonate to a 3‐bromooxindole to afford 3,3‐disubstituted oxindole, b) the formation of a 12‐membered cyclic enol ether by intramolecular O‐propargylation, immediately followed by propargyl Claisen rearrangement to provide the α‐allenyl ketone stereospecifically, c) DMDO oxidation to install a hydroxy group in a highly stereoselective manner, and d) the SmI₂‐mediated reductive C−O bond cleavage to remove the α‐keto carboxyl group.     

Collective Total Syntheses of Atisane‐Type Diterpenes and Atisine‐Type Diterpenoid Alkaloids: (±)‐Spiramilactone B, (±)‐Spiraminol, (±)‐Dihydroajaconine,and (±)‐Spiramines C and D

The first total syntheses of the architecturally complex atisane‐type diterpenes and biogenetically related atisine‐type diterpenoid alkaloids (±)‐spiramilactone B, (±)‐spiraminol, (±)‐dihydroajaconine, and (±)‐spiramines C and D are reported. Highlights of the synthesis include a late‐stage biomimetic transformation of spiramilactone B, a facile formal lactone migration from the pentacyclic skeleton of spiramilactone E, a highly efficient and diastereoselective 1,7‐enyne cycloisomerization to construct the functionalized tetracyclic atisane skeleton, and a tandem retro‐Diels–Alder/intramolecular Diels–Alder sequence to achieve the tricyclo[6.2.2.0] ring system.     

Total Synthesis of (−)‐Daphenylline

A concise and highly stereoselective total synthesis of the Daphniphyllum alkaloids (?)‐daphenylline has been accomplished. The synthesis was started from (S)‐carvone and proceeded via a stereoselective Mg(ClO₄)₂‐catalyzed intramolecular amide addition cyclization, an intramolecular Diels–Alder reaction to construct the ABCD tetracyclic core architecture, and a Robinson annulation coupled with an oxidative aromatization sequence. Finally, the DF ring system was installed through an intramolecular Friedel–Crafts cyclization. The total synthesis of (?)‐daphenylline is achieved in 19 steps in the longest reaction sequence and in 7.6 % overall yield.     

Total Synthesis of (−)‐Vindorosine

Outlined herein is a novel and scalable synthesis of (−)‐vindorosine based on two key transformations. A highly diastereoselective vinylogous Mannich addition of dioxinone‐derived lithium dienolates with indolyl N ‐tert‐butanesulfinyl imines has been developed. In addition, an intramolecular Heathcock/aza‐Prins cyclization was introduced to construct both the C, and the highly substituted E rings for the synthesis of (−)‐vindorosine and related alkaloids.     

A Concise Enantioselective Total Synthesis of (−)‐Virosaine A

The total synthesis of (−)‐virosaine A ( 1 ) was achieved in ten steps starting from furan and 2‐bromoacrolein. A one‐pot Diels–Alder cycloaddition/organolithium addition initiated an efficient sequence to access a key oxime/epoxide intermediate. Heating this intermediate in acetic acid resulted in an intramolecular epoxide opening/nitrone [3+2] cycloaddition cascade to construct the caged core of 1 in a single step. Several methods of C−H functionalization were assessed on the cascade product, and ultimately, a directed lithiation/bromination effected selective C14 functionalization, enabling the synthesis of 1 .