Rapid Construction of the ABCE Tetracyclic Tertiary Amine Skeleton in Daphenylline Enabled by an Amine–Borane Complexation Strategy

Enantioselective Total Synthesis of (-)-Daphenylline

A concise enantioselective total synthesis of (-)-daphenylline, a hexacyclic Daphniphyllum alkaloid with a unique benzene ring, was achieved in 14 steps. The synthesis commences with two chiral stereocenters, C2 and C18, readily installed via Carreira's Ir/amine dual-catalyzed allylation. The allylic bridgehead amine 6 was rapidly prepared through Wickens' photoredox-catalyzed hydrocarboxylation of olefin and CuBr2-catalyzed α-amination of ketone. The tetracycle 4 was formed via Pd-catalyzed reductive Heck reaction or, more concisely, by Krische's Rh-catalyzed reductive 1,6-enyne cyclization. In this synthesis, newly reported Wickens' photoredox-catalyzed hydrocarboxylation was used twice, and Friedel-Crafts acylation thrice.

Total Syntheses of Calyciphylline A-Type Alkaloids (-)-10-Deoxydaphnipaxianine A, (+)-Daphlongamine E and (+)-Calyciphylline R via Late-Stage Divinyl Carbinol Rearrangements

Among the famous Daphniphyllum alkaloids family, the calyciphylline A-type subfamily has triggered particular interest from the organic synthesis community in recent years. Here, we report divergent total syntheses of three calyciphylline A-type alkaloids, namely, (-)-10-deoxydaphnipaxianine A, (+)-daphlongamine E, and (+)-calyciphylline R. Our work highlights an efficient, divergent strategy via late-stage divinyl carbinol rearrangements, including an unprecedented oxidative Nazarov electrocyclization using an unfunctionalized tertiary divinyl carbinol and an unusual allylic alcohol rearrangement. A highly efficient "donor-acceptor" platinum catalyst was used for a critical nitrile hydration step. Moreover, the power of selective amide reductions has also been showcased by novel and classic tactics.

Synthesis of the ABC Ring of Calyciphylline A-Type Alkaloids by a Stereocontrolled Aldol Cyclization: Formal Synthesis of (±)-Himalensine A

A synthetic approach to a functionalized ABC-tricyclic framework of calyciphilline A-type alkaloids, a building block toward this class of alkaloids, is reported. The key synthetic steps involve a radical cyclization to form the hydroindole system and piperidine ring closure through a stereocontrolled aldol cyclization. The resulting alcohol allows the methyl group to be installed in the bowl-shaped azatricyclic structure; this crucial reaction takes place with configuration retention. The synthesis of azatricyclic compound I constitutes a formal synthesis of himalensine A.

Concise Enantioselective Total Synthesis of Daphenylline Enabled by an Intramolecular Oxidative Dearomatization

Daphenylline is a structurally unique member of the triterpenoid Daphniphyllum natural alkaloids, which exhibit intriguing biological activities. Six total syntheses have been reported, five of which utilize aromatization approaches. Herein, we report a concise protecting-group-free total synthesis by means of a novel intramolecular oxidative dearomatization reaction, which concurrently generates the critical seven-membered ring and the quaternary-containing vicinal stereocenters. Other notable transformations include a tandem reductive amination/amidation double cyclization reaction, to assemble the cage-like architecture, and installation of the other two chiral stereocenters via a highly enantioselective rhodium-catalyzed challenging hydrogenation of the diene intermediate (90% e.e.) and an unprecedented remote acid-directed Mukaiyama-Michael reaction of the complex benzofused cyclohexanone (13:1 d.r.).

A General Strategy for the Construction of Calyciphylline A-Type Alkaloids: Divergent Total Syntheses of (-)-Daphenylline and (-)-Himalensine A

An efficient general strategy for the synthesis of the Daphniphyllum alkaloids via the rapid construction of a common core intermediate has been established, based on which a divergent total synthesis of (-)-daphenylline and (-)-himalensine A has been accomplished in 16 and 19 steps, respectively. The present work features an enantioselective Mg(ClO₄ )₂ -catalyzed intramolecular amidocyclization to construct the aza-bridged core structure; a Cu-catalyzed intramolecular cyclopropanation and subsequent phosphine-catalyzed Cope-type rearrangement to furnish the himalensine A scaffold; and a one-pot Diels-Alder/aromatization method to assemble the aromatic skeleton of daphenylline.

Recent advances in total syntheses of natural products containing the benzocycloheptane motif

Covering: 2010 to 2020Benzocycloheptane is a fundamental and unique structural motif found in pharmaceuticals and natural products. The total syntheses of natural products bearing the benzocycloheptane subunit are challenging and there are only a few efficient approaches to access benzocycloheptane. Thus, new methods and innovative strategies for preparing such natural products need to be developed. In this review, recent progress in the total syntheses of natural products bearing the benzocycloheptane motif is presented, and key transformations for the construction of benzocycloheptane are highlighted. This review provides a useful guide for those engaged in the syntheses of natural products containing the benzocycloheptane motif.

A review on various aspects of organic synthesis using Comins' reagent

Recently, researchers have shown great interest in compounds such as triflate and enotriflate that are synthesized by Comins reagent. For the above-mentioned reason, we planned to review the works related to organic synthesis using Comins reagent. So this review includes a whole new investigation of the Comins reagent which is used for stereoselective conversion of α-keto ester, enolate to enol triflate of lactone and vinyl triflate to methyl ketone. Comins reagent plays an important role in regioselectivity such as transformations of ketone or dienolates into vinyl triflates and it has a major application in highly selective oxidation in an easy and environmentally friendly manner.

Total Synthesis of (-)-Daphnezomines A and B

Daphnezomines A and B are structurally unusual Daphniphyllum alkaloids that contain a unique aza-adamantane core skeleton. Herein, a modular approach to these alkaloids is presented that exploits a diverse array of reaction strategies. Commencing from a chiral pool terpene-(S)-carvone, the azabicyclo[3.3.1]nonane backbone, which occurs widely in Daphniphyllum alkaloids, was easily accessed through a Sharpless allylic amination and a palladium-catalyzed oxidative cyclization. A protecting group enabled a stereoselective B-alkyl Suzuki-Miyaura coupling sequence and an Fe-mediated hydrogen atom transfer (HAT)-based radical cyclization were then applied to construct C6 and C8 stereocenters. A final epimer locking strategy enabled the assembly of the highly congested aza-adamantane core, thereby achieving the first total synthesis of (-)-daphnezomines A and B in 14 steps.

Construction of the Tetracyclic Core of Calyciphylline B-Type Daphniphyllum Alkaloids

A double cyclization strategy was developed to construct the common tetracyclic core of calyciphylline B-type alkaloids. Key features of the synthesis included asymmetric Evans alkylation, ring-closing metathesis reaction, intermolecular amidation, intramolecular aza-Michael addition, and aldol condensation reactions. This strategy may be applied to the total syntheses of this type of natural product.

Enantioselective Total Synthesis of (-)-Caldaphnidine O via a Radical Cyclization Cascade

The synthetically challenging, diverse chemical skeletons and promising biological profiles of the Daphniphyllum alkaloids have generated intense interest from the synthetic chemistry community. Herein, the first and enantioselective total synthesis of (-)-caldaphnidine O, a complex bukittinggine-type Daphniphyllum alkaloid, is described. The key transformations in this concise approach included an intramolecular aza-Michael addition, a ring expansion reaction sequence, a Sm(II)/Fe(III)-mediated Kagan-Molander coupling, and the rapid formation of the entire hexacyclic ring skeleton of the target molecule via a radical cyclization cascade reaction, which was inspired by an unexpected radical detosylation observed in our recent dapholdhamine B synthesis.

Synthesis of the Core Structure of Daphnimacropodines

Daphniphyllum alkaloids daphnimacropodines A-C possess a highly congested ring system and share a common tetracyclic ring skeleton. To access the challenging chemical structure of daphnimacropodines, a divergent synthetic approach toward their total synthesis is described. A stereoselective synthesis of the core structure of daphnimacropodines has been achieved from a simple diketone building block. Our approach features an intramolecular carbamate aza-Michael addition and a hydropyrrole synthesis via a Au-catalyzed alkyne hydration followed by an aldol condensation, whereas all the other attempts failed.

Exploration of 1,3-dipolar cycloaddition reactions to construct the core skeleton of Calyciphylline A-type alkaloids

Nitrone induced 1,3-dipolar [3 + 2] cycloadditions were studied to construct the core structure of Calyciphylline A-type Daphniphyllum alkaloids.