Convergent and Efficient Total Synthesis of (+)-Heilonine Enabled by C-H Functionalizations

Ten-Step Total Synthesis of (±)-Phaeocaulisin A Enabled by Cyclopropanol Ring-Opening Carbonylation

We report an efficient total synthesis of (±)-phaeocaulisin A, a guaianolide sesquiterpene natural product possessing a complex tetracyclic skeleton embedded with an oxaspirolactone and a fused bicyclic lactone, four oxygen-containing stereocenters, and an 8-oxabicyclo[3.2.1]octane core. Our synthesis features a novel palladium-catalyzed cyclopropanol ring-opening carbonylation to access a key γ-ketoester, a chemo- and stereoselective aldol cyclization to form the seven-membered carbocycle, and a cascade ketalization-lactonization to construct the desired tetracyclic skeleton. With these strategically important C-C and C-O bond formation transformations, a 10-step total synthesis of (±)-phaeocaulisin A was achieved. We further developed the cyclopropanol ring-opening carbonylation chemistry to provide an alternative approach to prepare γ-ketoesters. Biologically, the penultimate intermediate with an α-methylene γ-butyrolactone moiety was identified as a promising lead compound with anticancer proliferation activity against a panel of triple-negative or HER2+ breast cancer cell lines.

Total Synthesis of the Hexacyclic Sesterterpenoid Niduterpenoid B via Structural Reorganization Strategy

To date, it remains challenging to precisely and efficiently construct structurally intriguing polycarbocycles with densely packed stereocenters in organic synthesis. Niduterpenoid B, a naturally occurring ERα inhibitor, exemplifies this complexity with its intricate polycyclic network comprising 5 cyclopentane and 1 cyclopropane rings, featuring 13 contiguous stereocenters, including 4 all-carbon quaternary centers. In this work, we describe the first total synthesis of niduterpenoid B using a structural reorganization strategy. Key features include the following: (1) an efficient methoxy-controlled cascade reaction that precisely forges a highly functionalized tetraquinane (A-D rings) bearing sterically hindered contiguous quaternary stereocenters; (2) a rhodium-catalyzed [1 + 2] cycloaddition that facilitates the construction of a strained 3/5 bicycle (E-F rings) angularly fused with ring D.

Divergent syntheses of complex Veratrum alkaloids

The Veratrum alkaloids are a class of highly intricate natural products renowned for their complex structural and stereochemical characteristics, which underlie a diverse array of pharmacological activities ranging from anti-hypertensive properties to antimicrobial effects. These properties have generated substantial interest among both synthetic chemists and biologists. While numerous advancements have been made in the synthesis of jervanine and veratramine subtypes over the past 50 years, the total synthesis of highly oxidized cevanine subtypes has remained relatively scarce. Building on the efficiency of our previously developed strategy for constructing the hexacyclic carbon skeleton of the Veratrum alkaloid family via a stereoselective intramolecular Diels-Alder reaction and radical cyclization, here we show the development of a unified synthetic approach to access highly oxidized Veratrum alkaloids. This includes the total synthesis of (-)-zygadenine, (-)-germine, (-)-protoverine and the alkamine of veramadine A, by capitalizing on a meticulously designed sequence of redox manipulations and a late-stage neighboring-group participation strategy.

Divergent and gram-scale syntheses of (-)-veratramine and (-)-cyclopamine

Veratramine and cyclopamine, two of the most representative members of the isosteroidal alkaloids, are valuable molecules in agricultural and medicinal chemistry. While plant extraction of these compounds suffers from uncertain supply, efficient chemical synthesis approaches are in high demand. Here, we present concise, divergent, and scalable syntheses of veratramine and cyclopamine with 11% and 6.2% overall yield, respectively, from inexpensive dehydro-epi-androsterone. Our synthesis readily provides gram quantities of both target natural products by utilizing a biomimetic rearrangement to form the C-nor-D-homo steroid core and a stereoselective reductive coupling/(bis-)cyclization sequence to establish the (E)/F-ring moiety.

Interrupted Corey-Chaykovsky Reaction of Tethered Bis-Enones to Access 2,3-Epoxy-hexahydrofluoren-9-ones

The Corey-Chaykovsky reaction is usually employed to synthesize cyclopropanes from activated olefins. We intercepted the intermediates prevailing during this transformation and diverted the process for the creation of intricate molecular motifs. We describe an unusual skeletal remodelling of tethered bis-enones to 2,3-epoxy-hexahydrofluoren-9-ones via an "interrupted Corey-Chaykovsky reaction". The strategy rationally merges the nucleophilic features of sulfur ylides with electronically biased olefins to achieve the regio- and stereoselective synthesis of several new classes of hydrofluorenones. We have demonstrated the synthetic utility of the products in accessing several highly functionalized molecules.

Synthesis of the DEF-Ring Spirocyclic Core of Cyclopamine

A stereoselective synthesis of the DEF-ring spirocyclic core of cyclopamine was accomplished using commercially available materials. The key steps in the synthesis were (i) the enantioselective vinylogous Mannich reaction, followed by lactamization to generate the piperidine F ring, and (ii) intramolecular oxidative dearomative spiroetherification to construct the DEF-ring spirocyclic core of cyclopamine. We found that the stereochemistry of the spirocyclization was controlled by the configuration of the methyl group (C-20) in the substrate.