Expedient catalytic construction of azabicyclo[4.1.0]/[5.1.0] carbaldehydes via intramolecular cyclopropanation

Total Synthesis of (-)-Rauvomine B via a Strain-Promoted Intramolecular Cyclopropanation

We describe the first total synthesis of the unusual cyclopropane-containing indole alkaloid (-)-rauvomine B via a strategy centered upon intramolecular cyclopropanation of a tetracyclic N-sulfonyltriazole. Preparation of this precursor evolved through two generations of synthesis, with the ultimately successful route involving a palladium-catalyzed stereospecific allylic amination, a cis-selective Pictet-Spengler reaction, and ring-closing metathesis as important bond-forming reactions. The key cyclopropanation step was found to be highly dependent on the structure and conformational strain of the indoloquinolizidine N-sulfonyltriazole precursor, the origins of which are explored computationally through DFT studies. Overall, our synthesis proceeds in 11 total steps and 2.4% yield from commercial materials.

Diastereoselective Synthesis of Highly Functionalized Proline Derivatives

An efficient way to access highly functionalized proline derivatives was developed based on a Cu(I)-catalyzed reaction between CF₃-substituted allenynes and tosylazide, which involved a cascade of [3 + 2]-cycloaddition/ketenimine and a rearrangement/Alder-ene cyclization to afford the new proline framework with a high diastereoselectivity.

Rhodium (II)-Catalyzed Synthesis of Tetracyclic 3,4-Fused Indoles and Dihydroindoles

An efficient synthetic method of tetracyclic 3,4-fused indoles and dihydroindoles via rhodium-catalyzed (3+2) cycloaddition of N-tosyl-4-(2-phenoxyphenyl)-1,2,3-triazole was described. The aromatized xanthene derivatives can be achieved in a one-pot synthesis starting from 1-ethynyl-2-phenoxybenzene. The xanthene-based fused heterocycles were considered as the valuable fluorophore.

Synthesis of adenine dinucleosides SAM analogs as specific inhibitors of SARS-CoV nsp14 RNA cap guanine-N7-methyltransferase

The spreading of new viruses is known to provoke global human health threat. The current COVID-19 pandemic caused by the recently emerged coronavirus SARS-CoV-2 is one significant and unfortunate example of what the world will have to face in the future with emerging viruses in absence of appropriate treatment. The discovery of potent and specific antiviral inhibitors and/or vaccines to fight these massive outbreaks is an urgent research priority. Enzymes involved in the capping pathway of viruses and more specifically RNA N7- or 2′O-methyltransferases (MTases) are now admitted as potential targets for antiviral chemotherapy. We designed bisubstrate inhibitors by mimicking the transition state of the 2′-O-methylation of the cap RNA in order to block viral 2′-O MTases. This work resulted in the synthesis of 16 adenine dinucleosides with both adenosines connected by various nitrogen-containing linkers. Unexpectedly, all the bisubstrate compounds were barely active against 2′-O MTases of several flaviviruses or SARS-CoV but surprisingly, seven of them showed efficient and specific inhibition against SARS-CoV N7-MTase (nsp14) in the micromolar to submicromolar range. The most active nsp14 inhibitor identified is as potent as but particularly more specific than the broad-spectrum MTase inhibitor, sinefungin. Molecular docking suggests that the inhibitor binds to a pocket formed by the S-adenosyl methionine (SAM) and cap RNA binding sites, conserved among SARS-CoV nsp14. These dinucleoside SAM analogs will serve as starting points for the development of next inhibitors for SARS-CoV-2 nsp14 N7-MTase.

Grubbs catalysts in intramolecular carbene C(sp3)-H insertion reactions from α-diazoesters

Grubbs catalysts are described as a useful alternative to promote intramolecular carbene C-H insertion from α-diazoesters. Moreover, no competition arises from the possible metathesis reactions on substrates bearing alkene and alkyne moieties. DFT calculations were also carried out to gain insight into the reaction mechanism involved in these transformations.

The Expanding Utility of Rhodium-Iminocarbenes: Recent Advances in the Synthesis of Natural Products and Related Scaffolds

Rhodium-iminocarbenes that are derived from N-sulfonyl-1,2,3-triazoles have become an important class of reactive species and useful intermediates in organic synthesis. Over the last several years, many practical and versatile approaches involving rhodium-iminocarbene intermediates to synthetically challenging molecules (scaffolds) have been developed. This Minireview mainly summarizes the recent advance of rhodium-iminocarbene involved reactions in the synthesis of natural products and their related scaffolds by the end of 2017. Several applications in important pharmaceuticals are documented as well.

Straightforward regioselective construction of 3,4-dihydro-2H-1,4-thiazine by rhodium catalysed [3 + 3] cycloaddition of thiirane with 1-sulfonyl-1,2,3-triazole: a pronounced acid additive effect

A rhodium catalyzed regioselective coupling of thiirane with 1-sulfonyl-1,2,3-triazole has been realized to give a formal [3 + 3] cycloaddition product 3,4-dihydro-2H-1,4-thiazine via the 1,3-insertion model of azavinyl carbene.