Total Synthesis of (-)-Elodeoidins A and B

Biomimicry has long been a valuable approach for designing efficient synthetic strategies in complex natural product synthesis. However, abiotic yet powerful transforms can significantly streamline the synthesis by introducing greater convergence to the synthetic route. Herein, we delineate a convergent total synthesis of elodeoidins A and B, enabled by a cross-dehydrogenative coupling (CDC) reaction between an aldehyde and an electron-deficient olefin. The CDC reaction operating under the newly discovered reaction conditions proceeds via distinct concerted deprotonation within the formal Cu(III) catalytic complex. Furthermore, the total synthesis of both structural candidates of elodeoidin B revealed that the natural product exists as a mixture of epimers at the C8 stereocenter.

Carbonylative cyclization of biaryl enones with aldehydes and oxamic acids

An oxidative radical-promoted carbonylative cyclization strategy for the synthesis of phenanthren-9-(10H)-one frameworks from biaryl enones using aldehydes as the carbonyl radical sources is disclosed. The reaction proceeds through a sequential addition of a carbonyl radical to the olefin followed by cyclization with an aryl ring. The method is further extended to carbamoyl radicals generated from oxamic acids to access the corresponding phenanthrenones with amide functionalities.

Visible Light-Induced Metal-free Arylation of Coumarin-3-carboxylates with Arylboronic Acids

The present work represents a novel methodology for the selective arylation of coumarin-3-carboxylates with arylboronic acids via a photochemical route, marking the first-ever attempt for the direct alkenyl C-H arylation using rose bengal as a photocatalyst, which is a readily available and cost-effective alternative to transition metal catalysis. The reaction proceeds smoothly in MeOH/H2O solvent media in the presence of radical initiator affording the arylated products in good yields (60-80 %). The reaction parameters such as visible light, radical initiator, oxidant, anhydrous solvent, and inert atmosphere play a crucial role for the success of this methodology. The substituents present on the substrate show a significant effect on the conversion. This study provides a valuable contribution to the field of organic synthesis offering a new and efficient approach to the arylation of coumarin-3-carboxylic acid esters with a broad substrate scope and high functional group tolerance. It is a versatile method and provides a direct access to biologically relevant 4-arylcoumarin-3-carboxylates.

Visible Light-Induced Cross-Dehydrocoupling of 3-Cyanocoumarins with Unactivated Aliphatic Aldehydes Enables Access to 4-Acylated Coumarins

We report visible light-induced cross-dehydrocoupling of 3-cyanocoumarins with unactivated aliphatic aldehydes for the direct synthesis of 4-acylated coumarins. Inexpensive and readily available (n-Bu)₄NBr was used as a precursor of the hydrogen atom transfer (HAT) catalyst and [Ir(ppy)₂(dtbbpy)PF₆] as a photocatalyst. A variety of aldehydes including linear, branched, cyclic, and α,β-unsaturated aliphatic aldehydes were suitable for this reaction yielding the desired acylated coumarin derivatives in 41-98% yields. This method provides a mild, atom-economical, and environmentally friendly synthetic route for the direct acylation of 3-cyanocoumarins. This is the first example so far of C-4 aliphatic acylation of coumarins.

Synthesis of Dimeric Securinega Alkaloid Flueggeacosine B: From Pd-Catalyzed Cross-Coupling to Cu-Catalyzed Cross-Dehydrogenative Coupling

We completed the synthesis of dimeric high-oxidation-state securinega alkaloid flueggeacosine B via two synthetic routes from allosecurinine. The first-generation synthesis (seven overall steps) involved a Liebeskind-Srogl cross-coupling reaction for the union of two functionalized fragments, the organostannane and the thioester. As a means to further streamline the synthetic route, we have developed a visible-light-mediated Cu-catalyzed cross-dehydrogenative coupling (CDC) reaction between an aldehyde and an electron-deficient olefin. This enabled the second-generation synthesis of flueggeacosine B from allosecurinine in four overall steps. The newly developed CDC reaction paves a direct way to a conjugated dicarbonyl moiety, a ubiquitous structural moiety present in various natural products.

Recent advances in acyl radical enabled reactions between aldehydes and alkenes

Radical-mediated functionalization of alkenes has been emerging as an elegant and straightforward protocol to increase molecule complexity. Moreover, the abstraction of a hydrogen atom from aldehydes to afford acyl radicals has evolved as a rising star due to its high atom-economy and the ready availability of aldehydes. Considering the great influence and synthetic potential of acyl radical enabled reactions between aldehydes and alkenes, we provide a summary of the state of the art in this field with a specific emphasis on the working models and corresponding mechanisms. The discussion is divided according to the kind of alkenes and reaction type.

The recent advances in K2S2O8-mediated cyclization/coupling reactions via an oxidative transformation

Recently the K₂S₂O₈ mediated cyclization/coupling reactions to construct carbon–carbon/carbon–heteroatom bond via oxidative transformation is became much interesting in organic synthesis.

Metal-free, radical 1,6-conjugated addition of cyclic ethers with para-quinone methides (p-QMs)

An efficient method for metal-free C–C bond formation between p-quinone methides (p-QMs) and cyclic ethers via a radical pathway to afford substituted diarylmethanes and triarylmethanes or to effect the α-alkylation of the cyclic ethers has been developed.