Toward the Synthesis of Yuzurimine-Type Alkaloids: Stereoselective Construction of the Heterocyclic Portions of Deoxyyuzurimine and Macrodaphnine

Mitsunobu Reaction: A Powerful Tool for the Synthesis of Natural Products: A Review

The Mitsunobu reaction plays a vital part in organic chemistry due to its wide synthetic applications. It is considered as a significant reaction for the interconversion of one functional group (alcohol) to another (ester) in the presence of oxidizing agents (azodicarboxylates) and reducing agents (phosphines). It is a renowned stereoselective reaction which inverts the stereochemical configuration of end products. One of the most important applications of the Mitsunobu reaction is its role in the synthesis of natural products. This review article will focus on the contribution of the Mitsunobu reaction towards the total synthesis of natural products, highlighting their biological potential during recent years.

Synthesis of the [6.6.7.5] Tetracyclic Core of Calyciphylline N via a Boc-Mediated Oxidative Dearomatization/Diels-Alder Approach

A sequential process involving Boc-mediated oxidative dearomatization and inter/intramolecular Diels-Alder reaction was investigated. Based on an intermolecular Diels-Alder reaction and subsequently a radical 7-endo-trig type cyclization, the [6.6.7.5] tetracyclic core of Calyciphylline N was assembled.

Formal total synthesis of dankasterone B

A formal total synthesis of dankasterone B was achieved in 15 steps.

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.

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.

Asymmetric total synthesis of yuzurimine-type Daphniphyllum alkaloid (+)-caldaphnidine J

Ever since Hirata’s report of yuzurimine in 1966, nearly fifty yuzurimine-type alkaloids have been isolated, which formed the largest subfamily of the Daphniphyllum alkaloids. Despite extensive synthetic studies towards this synthetically challenging and biologically intriguing family, no total synthesis of any yuzurimine-type alkaloids has been achieved to date. Here, the first enantioselective total synthesis of (+)-caldaphnidine J, a highly complex yuzurimine-type Daphniphyllum alkaloid, is described. Key transformations of this approach include a highly regioselective Pd-catalyzed hydroformylation, a samarium(II)-mediated pinacol coupling, and a one-pot Swern oxidation/ketene dithioacetal Prins reaction. Our approach paves the way for the synthesis of other yuzurimine-type alkaloids and related natural products.

Despite being known for more than 50 years, yuzurimine-type alkaloids have not been accessed by total synthesis. Here, the authors report the first enantioselective total synthesis of (+)-Caldaphnidine J, a highly complex yuzurimine-type Daphniphyllum alkaloid.

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.

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.