Four-step synthesis of the antimalarial cardamom peroxide via an oxygen stitching strategy

Ph(i-PrO)SiH2: An Exceptional Reductant for Metal-Catalyzed Hydrogen Atom Transfers

We report the discovery of an outstanding reductant for metal-catalyzed radical hydrofunctionalization reactions. Observations of unexpected silane solvolysis distributions in the HAT-initiated hydrogenation of alkenes reveal that phenylsilane is not the kinetically preferred reductant in many of these transformations. Instead, isopropoxy(phenyl)silane forms under the reaction conditions, suggesting that alcohols function as important silane ligands to promote the formation of metal hydrides. Study of its reactivity showed that isopropoxy(phenyl)silane is an exceptionally efficient stoichiometric reductant, and it is now possible to significantly decrease catalyst loadings, lower reaction temperatures, broaden functional group tolerance, and use diverse, aprotic solvents in iron- and manganese-catalyzed hydrofunctionalizations. As representative examples, we have improved the yields and rates of alkene reduction, hydration, hydroamination, and conjugate addition. Discovery of this broadly applicable, chemoselective, and solvent-versatile reagent should allow an easier interface with existing radical reactions. Finally, isotope-labeling experiments rule out the alternative hypothesis of hydrogen atom transfer from a redox-active β-diketonate ligand in the HAT step. Instead, initial HAT from a metal hydride to directly generate a carbon-centered radical appears to be the most reasonable hypothesis.

Markovnikov free radical addition reactions, a sleeping beauty kissed to life

This review covers free radical additions, which are initiated by the formal addition of a hydrogen atom to a C[double bond, length as m-dash]C double bond. These reactions originated in the realms of inorganic chemistry, polymer chemistry, and organic chemistry, whereby barriers between these disciplines impeded the rapid implementation of the findings.

Preparation of Antimalarial Endoperoxides by a Formal [2 + 2 + 2] Cycloaddition

A formal [2 + 2 + 2] cycloaddition reaction between a 1,3-dione, an olefin, and molecular oxygen mediated by light is reported, which delivers endoperoxides in good yield through the formation of two C-O and one C-C bond in one step. The resulting 1,2-dioxanes are stable compounds and can be further derivatized at the hemiacetal position via alkylation or acetylation. All compounds have been evaluated against Plasmodium falciparum, and the best compound displayed an IC50-value of 180 nM. A potential mechanistic rationale for the formation of these compounds is presented.

Total Synthesis of Verruculogen and Fumitremorgin A Enabled by Ligand-Controlled C-H Borylation

Verruculogen and fumitremorgin A are bioactive alkaloids that contain a unique eight-membered endoperoxide. Although related natural products such as fumitremorgins B and C have been previously synthesized, we report the first synthesis of the more complex, endoperoxide-containing members of this family. A concise route to verruculogen and fumitremorgin A relied not only on a hydroperoxide/indole hemiaminal cyclization, but also on the ability to access the seemingly simple starting material, 6-methoxytryptophan. An iridium-catalyzed C-H borylation/Chan-Lam procedure guided by an N-TIPS group enabled the conversion of a tryptophan derivative into a 6-methoxytryptophan derivative, proving to be a general way to functionalize the C6 position of an N,C3-disubstituted indole for the synthesis of indole-containing natural products and pharmaceuticals.

An SN1-type Reaction To Form the 1,2-Dioxepane Ring: Synthesis of 10,12-Peroxycalamenene

The synthesis of the sesquiterpene endoperoxide natural product 10,12-peroxycalamenene has been achieved. Featured transformations include an intramolecular Heck reaction to build the fused bicyclic core and a cobalt-catalyzed peroxidation to install the peroxide functional group. The final step involved an SN1-type ring closure catalyzed by DDQ to construct the 1,2-dioxepane ring.

Hydromethylation of Unactivated Olefins

A solution to the classic unsolved problem of olefin hydromethylation is presented. This highly chemoselective method can tolerate labile and reactive chemical functionalities and uses a simple set of reagents. An array of olefins, including mono-, di-, and trisubstituted olefins, are all smoothly hydromethylated. This mild protocol can be used to simplify the synthesis of a specific target or to directly “edit” complex natural products and other advanced materials. The method is also amenable to the simple installation of radioactive and stable labeled methyl groups.

Antimalarial chemotherapy: orally curative artemisinin-derived trioxane dimer esters

Eight new artemisinin-derived trioxane dimer esters 5 have been prepared and tested for antimalarial efficacy in malaria-infected mice. At a single oral dose of only 6mg/kg combined with 18mg/kg of mefloquine, each of the dimer esters 5 outperformed the antimalarial drug artemether (2). The most efficacious dimer, dichlorobenzoate ester 5h, prolonged mouse survival past day 30 of infection with three of the four mice in this group having no detectable parasitemia and appearing and acting healthy on day 30.

Expeditious entry to the chamigrane endoperoxide family of natural products

Several members of the recently reported peroxy chamigrane family of natural products were synthesized via a distereoselective route with a novel facial-selective epoxidation of a spiroundecadiene, a facile epoxide rearrangement, and a Co(II)-mediated silylperoxidation as the key steps. Adaptation of the diastereoselective route to an enantioselective one is also illustrated.

Copper(i)-promoted cycloalkylation–peroxidation of unactivated alkenes via sp3C–H functionalisation

A copper-promoted cycloalkylation–peroxidation strategy has been developedviaa three-component reaction involving cycloalkanes,tert-butyl hydroperoxide and internal conjugated alkene.

Activation of aqueous hydrogen peroxide for non-catalyzed dihydroperoxidation of ketones by azeotropic removal of water

Cyclic and acyclic ketones were selectively converted to gem-dihydroperoxides in 72–99% yield with 30% aq. hydrogen peroxide by azeotropic distillation of water from the reaction mixture without any catalyst.