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.

Enantioselective Total Synthesis of (-)-Zygadenine.

The Veratrum alkaloids are highly complex steroidal alkaloids characterized by their intricate structural and stereochemical features and exhibit a diverse range of pharmacological activities. A new synthetic pathway has been developed to access this family of natural products, which enabled the first total synthesis of (-)-zygadenine. This synthetic route entails the construction of a hexacyclic carbon skeleton through a stereoselective intramolecular Diels-Alder reaction, followed by a radical cyclization. Subsequently, a meticulously designed sequence of redox manipulations was optimized to achieve the de novo synthesis of this highly oxidized Veratrum alkaloid.

Total Synthesis of (+)-Isolysergol.

The enantioselective synthesis of (+)-isolysergol was completed in 18 steps, and an overall yield of 11% was obtained from (2R)-(+)-phenyloxirane as a chiral pool. Key features of the synthesis include a stereoselective intramolecular 1,3-dipolar addition of nitrone with terminal olefin and a Cope elimination to furnish the D ring. A rhodium-catalyzed intramolecular [3 + 2] annulation of a benzene ring with α-imino carbenoid was designed to afford the 3,4-fused indole scaffold at the late stage of the synthesis.

Dealkenylative Ni-Catalyzed Cross-Coupling Enabled by Tetrazine and Photoexcitation.

A new and general method to functionalize the C(sp3)-C(sp2) bond of alkyl and alkene linkages has been developed, leading to the dealkenylative generation of carbon-centered radicals that can be intercepted to undergo Ni-catalyzed C(sp3)-C(sp2) cross-coupling. This one-pot protocol leverages the easily procured alkene feedstocks for organic synthesis with excellent functional group compatibility without the need for a photoredox catalyst.

Total Synthesis of (-)-Batrachotoxinin A: A Local-Desymmetrization Approach.

An enantioselective total synthesis of (-)-batrachotoxinin A is accomplished based on a key photoredox coupling reaction and the subsequent local-desymmetrization operation. After the expedient assembly of the highly oxidized steroid skeleton, a delicate sequence of redox manipulations was carried out to deliver a late-stage intermediate on gram scale-and ultimately (-)-batrachotoxinin A in an efficient manner.

Total Synthesis of (-)-Chanoclavine I and an Oxygen-Substituted Ergoline Derivative.

An efficient and direct route to ergot alkaloid (-)-chanoclavine I (3) is described using the inexpensive compound (2R)-(+)-phenyloxirane (15) as a chiral pool in 13 steps with 17% overall yield. Key features of the synthesis include a palladium-catalyzed intramolecular aminoalkynylation of terminal olefin and a rhodium-catalyzed intramolecular [3 + 2] annulation. An oxygen-substituted ergoline derivative (-)-25 was also achieved by using the same strategy.

Formal synthesis of (±)-cycloclavine.

An efficient formal synthesis of (±)-cycloclavine is achieved in seven steps and 27% overall yield from the known 2-(4-bromo-1-tosyl-1H-indol-3-yl)acetaldehyde. Key features include an iron(III)-catalyzed aza-Cope-Mannich cyclization and an intramolecular Heck reaction or a self-terminating 6-exo-trig aryl radical-alkene cyclization.