Enantioselective Total Synthesis of Berkeleyone A and Preaustinoids

Evolution of a Strategy for the Unified, Asymmetric Total Syntheses of DMOA-Derived Spiromeroterpenoids

DMOA-derived spiromeroterpenoids are a group of natural products with complex structures and varied biological activities. Recently, we reported the first enantioselective total synthesis of five spiromeroterpenoids based on a fragment coupling strategy. This full account describes details of a strategy evolution that culminated in successful syntheses of the targeted natural products. Although our alkylative dearomatization methodology was unable to deliver the desired spirocyclic products in our first-generation approach, our second-generation approach based on oxidative [3 + 2] cycloaddition produced the asnovolin H core along with several complex dimers. Challenges with the dearomatization approach finally led us to develop a third generation, non-dearomatization approach based on a fragment coupling strategy to construct the conserved, sterically hindered bis-neopentyl linkage of the spiromeroterpenoids through 1,2-addition. To enable scalable access of the natural products, a refined, multigram-scale synthesis of the coupling partners was developed. A series of stereoselective transformations were developed through judicious choice of reagents and conditions. Finally, modular spirocycle construction logic was demonstrated through the synthesis of a small library of spiromeroterpenoid analogues.

Controllable skeletal reorganizations in natural product synthesis

Covering: 2016 to 2023The synthetic chemistry community is always in pursuit of efficient routes to natural products. Among the many available general strategies, skeletal reorganization, which involves the formation, cleavage, and migration of C-C and C-heteroatom bonds, stands out as a particularly useful approach for the efficient assembly of molecular skeletons. In addition, it allows for late-stage modification of natural products for quick access to other family members or unnatural derivatives. This review summarizes efficient syntheses of steroid, terpenoid, and alkaloid natural products that have been achieved by means of this strategy in the past eight years. Our goal is to illustrate the strategy's potency and reveal the spectacular human ingenuity demonstrated in its use and development.

Bioinspired Total Synthesis of Hyperireflexolides A and B

Hyperireflexolides A and B were synthesized in six steps via the dearomatization and fragmentation of a simple acylphloroglucinol starting material. The dearomatized acylphloroglucinol undergoes a sequence of oxidative radical cyclization, retro-Dieckmann fragmentation, stereodivergent intramolecular carbonyl-ene reactions, and final α-hydroxy-β-diketone rearrangements to give the target natural products. This sequence is based on a biosynthetic proposal that claims the hyperireflexolides as highly rearranged polycyclic polyprenylated acylphloroglucinols (PPAPs), which is supported by the structural revision of hyperireflexolide B.

Sharpless Asymmetric Dihydroxylation: An Impressive Gadget for the Synthesis of Natural Products: A Review

Sharpless asymmetric dihydroxylation is an important reaction in the enantioselective synthesis of chiral vicinal diols that involves the treatment of alkene with osmium tetroxide along with optically active quinine ligand. Sharpless introduced this methodology after considering the importance of enantioselectivity in the total synthesis of medicinally important compounds. Vicinal diols, produced as a result of this reaction, act as intermediates in the synthesis of different naturally occurring compounds. Hence, Sharpless asymmetric dihydroxylation plays an important role in synthetic organic chemistry due to its undeniable contribution to the synthesis of biologically active organic compounds. This review emphasizes the significance of Sharpless asymmetric dihydroxylation in the total synthesis of various natural products, published since 2020.

Seven new meroterpenoids from the fungus Penicillium sclerotiorum GZU-XW03-2

Seven previously undescribed meroterpenoids, peniscmeroterpenoids H - N (1-7), were isolated from the marine-derived fungus Penicillium sclerotiorum GZU-XW03-2. Their structures were established by the spectroscopic methods and the electronic circular dichroism (ECD) calculations. Peniscmeroterpenoid H was a 6/6/6/5/6 rearranged pentacyclic meroterpenoid, featuring a unique 2-oxaspiro[5.5] undeca-4,7-dien-3-one motif. Peniscmeroterpenoids I and J (2 and 3) owned rare 6(D)/5(E) fused rings were not common in natural products, and compound 2 was the second example of a berkeleyone analogue stripped of the methyl ester fragment. Peniscmeroterpenoid K (4) was the first case where the C-24 was oxidized. In bioassay, compound 5 showed moderate anti-inflammatory activity.

Ring contraction in synthesis of functionalized carbocycles

Carbocycles are a key and widely present structural motif in organic compounds. The construction of structurally intriguing carbocycles, such as highly-strained fused rings, spirocycles or highly-functionalized carbocycles with congested stereocenters, remains challenging in organic chemistry. Cyclopropanes, cyclobutanes and cyclopentanes within such carbocycles can be synthesized through ring contraction. These ring contractions involve re-arrangement of and/or small molecule extrusion from a parental ring, which is either a carbocycle or a heterocycle of larger size. This review provides an overview of synthetic methods for ring contractions to form cyclopropanes, cyclobutanes and cyclopentanes en route to structurally intriguing carbocycles.

Short, Divergent, and Enantioselective Total Synthesis of Bioactive ent-Pimaranes

We present the first total synthesis of eight ent-pimaranes via a short and enantioselective route (11-16 steps). Key features of the divergent synthesis are a Sharpless asymmetric dihydroxylation, a Brønsted acid catalyzed cationic bicyclization, and a mild Rh-catalyzed arene hydrogenation for rapid access to a late synthetic branching point. From there on, selective functional group manipulations enable the synthesis of ent-pimaranes bearing different modifications in the A- and C-rings.

Intramolecular Tricarbonyl-Ene Reactions and α-Hydroxy-β-Diketone Rearrangements Inspired by the Biosynthesis of Polycyclic Polyprenylated Acylphloroglucinols

Structurally unique natural products pose biosynthetic puzzles whose solution can inspire new chemical reactions. Herein, we propose a unified biosynthetic pathway towards some complex meroterpenoids-the hyperireflexolides, biyoulactones, hybeanones and hypermonones. This hypothesis led to the discovery of uncatalyzed, intramolecular carbonyl-ene reactions that are spontaneous at room temperature. We also developed an anionic cascade reaction featuring an α-hydroxy-β-diketone rearrangement and an intramolecular aldol reaction to access four distinct natural product scaffolds from a common intermediate.

The N-heterocyclic carbene-catalyzed [3 + 2] annulation of isoindigos with enals: the enantioselective construction of three contiguous stereogenic centers

An NHC-catalyzed enantioselective [3 + 2] annulation of enals and isoindigo is introduced as an efficient strategy for the construction of dimeric spirocyclic bisindoline alkaloid derivatives with moderate yields and good enantioselectivities.

Reductive Radical Annulation Strategy toward Bicyclo[3.2.1]octanes: Synthesis of ent-Kaurane and Beyerane Diterpenoids

Here we report a general [3 + 2] radical annulation that allows the facile construction of bicyclo[3.2.1]octane motifs in ent-kaurane- and beyerane-type diterpenoids. This radical annulation is difficult to control but was realized by harnessing an unprecedented and counterintuitive effect of TEMPO. Eleven natural products with a wide array of oxidation states are easily prepared, demonstrating the powerful utility of this straightforward synthetic strategy.

Synthetic Studies toward the Berkeleyacetal Core Architecture

Berkeleyacetals are structurally complex natural products that have shown potent anti-inflammatory activity. The presence of a highly dense oxygen functionality and a polycyclic ring system presents significant synthetic challenges. Herein, we report an efficient strategy for the construction of the tetracyclic core system of berkeleyacetal. Our synthetic strategy features two cycloadditions ([4+2] and [5+2]) to forge the tetracyclic core and Achmatowicz rearrangement for the preparation of the cyclization substrates containing B and E rings.