Syntheses of Gymnothespirolignans B and C and Non-natural Isomer 9-Epi-gymnothespirolignan B

Total synthesis of breviscapin B via intramolecular dehydrative etherification

The total synthesis of breviscapin B, a norlignan natural product having an unusual 2,2-diaryltetrahydrofuran skeleton, has been achieved via intramolecular dehydrative Williamson ether synthesis as a key step. The use of a combination of p-TsOH·H2O and polyfluorinated alcohol was found as an effective method for the synthesis of 2-aryl-substituted saturated oxygen heterocycles.

Asymmetric Total Synthesis of Gymnothespirolignan A via a Bioinspired Double Cyclization Approach

The first asymmetric total synthesis of gymnothespirolignan A is disclosed in 11 steps. The salient feature of the synthesis is construction of the spirocyclic moiety through a bioinspired acid-promoted double cyclization of an acyclic gymnothebutyllignan A-like precursor, which involves a deprotection, hemiketalization, dehydrative oxonium formation, and Friedel-Crafts cyclization cascade transformation. This study provides a general approach to the asymmetric syntheses of novel spirocyclic gymnothelignans.

Synthesis of the Phormidolide A Macrocycle Supports the Proposed Configurational Reassignment

We describe the successful synthesis of the phormidolide A macrocycle as a crucial step toward its total synthesis and configurational assignment. Exhaustive exploration of macrocyclization strategies revealed the detrimental effects of a bulky protecting group on the C17 hydroxyl function, leading to the successful use of a C17 p-methoxybenzyloxymethyl (PMBM) ether in the macrolactonization reaction. Further elaboration of the macrocycle with a truncated C18-C23 side chain afforded an advanced C1-C23 fragment of phormidolide A. Detailed comparison of spectroscopic data with those of phormidolide A supports the proposed configurational reassignment.

A Domino Radical Amidation/Semipinacol Approach to All-Carbon Quaternary Centers Bearing an Aminomethyl Group

A photoredox-mediated radical amidation ring-expansion sequence that enables the generation of all-carbon quaternary centers bearing a protected aminomethyl substituent is described. The methodology can be applied to both styrene and unactivated alkene substrates generating structurally diverse sp3 -rich amine derivatives in a concise manner.

Late-Stage Functionalization: Total Synthesis of Beauveamide A and Its Congeners and Their Anticancer Activities

Asymmetric total synthesis of cyclotetradepsipeptide beauveamide A has been achieved for the first time. A macrolactamization strategy involving two possible sites has been explored to find the most effective route for cyclization. A late-stage functionalization approach has been adopted for easy access of non-natural analogues of beauveamide A for further biological evaluation. Interestingly, the anticancer activity of one of the synthesized analogues was better than that of the parent natural product.

Direct Assembly of Diverse Unsymmetrical Tertiary 9-Fluorenols via Transient Directing Group-Enabled Palladium-Catalyzed Dual C-H Bond Activation of α-Ketoesters

An expeditious construction of an unsymmetrical tertiary 9-fluorenol skeleton was accomplished starting from readily available α-ketoester and aryl iodide. Inexpensive commercially available substituted aniline was utilized as a potent monodentate transient directing group (TDG) to assist palladium-catalyzed direct ortho-C-H arylation and tandem dual C-H activation of α-ketoesters to form two carbon-carbon bonds. To demonstrate practical applications, the reaction was enlarged to the gram scale, and subsequent one-step derivatization allowed facile access to structurally diversified useful derivatives. A series of control experiments were carried out to shed light on the possible catalytic mechanism.