Chiral Acetal-Based Stereo-Controlled Degradable Polymer Synthesis.

The precise synthesis of chiral polymers remains a significant challenge in polymer chemistry, particularly for applications in advanced biomedical and electronic materials. The development of degradable polymers is important for eco-friendly and advanced materials. Here, we introduce a stereo-controlled degradable polymer via cascade enyne metathesis polymerization and enantioselective acetal synthesis through Pd-catalyzed asymmetric hydroamination. This approach allows for the creation of chiral acetal-based polymers with controlled stereochemistry and degradability, highlighting their potential for use in drug delivery and electronic applications. This concept article reviews the background, development, and potential applications of these stereo-controlled degradable polymers.

Asymmetric Total Synthesis of Chaetoglobin A.

An asymmetric total synthesis of chaetoglobin A was achieved. Atroposelective oxidative coupling of a phenol incorporating all but one carbon of the final product was used as a key step to generate axial chirality. The stereochemical outcome of the catalytic oxidative phenolic with the highly substituted phenol used herein was found to be opposite that of the simpler congeners reported previously, providing a cautionary tale about extrapolating asymmetric processes from simple to more complex substrates. Optimization of the postphenolic coupling steps including formylation, oxidative dearomatization, and selective deprotection steps are outlined. The tertiary acetates of chaetoglobin A were exceptionally labile due to activation by the adjacent keto groups, which complicated each of these steps. In contrast, the final oxygen to nitrogen exchange proceeded readily and the spectroscopic data from the synthetic material matches that of the isolated natural product in all respects.

Enantioselective Vanadium-Catalyzed Oxidative Coupling: Development and Mechanistic Insights.

The evolution of a more reactive chiral vanadium catalyst for enantioselective oxidative coupling of phenols is reported, ultimately resulting in a simple monomeric vanadium species combined with a Brønsted or Lewis acid additive. The resultant vanadium complex is found to effect the asymmetric oxidative ortho-ortho coupling of simple phenols and 2-hydroxycarbazoles with good to excellent levels of enantioselectivity. Experimental and quantum mechanical studies of the mechanism indicate that the additives aggregate the vanadium monomers. In addition, a singlet to triplet crossover is implicated prior to carbon-carbon bond formation. The two lowest energy diastereomeric transition states leading to the enantiomeric products differ substantially with the path to the minor enantiomer involving greater torsional strain between the two phenol moieties.

Stability of Zr-Based UiO-66 Metal-Organic Frameworks in Basic Solutions.

Although Zr-based metal-organic frameworks (MOFs) exhibit robust chemical and physical stability in the presence of moisture and acidic conditions, their susceptibility to nucleophilic attacks from bases poses a critical challenge to their overall stability. Herein, we systematically investigate the stability of Zr-based UiO-66 (UiO = University of Oslo) MOFs in basic solutions. The impact of 11 standard bases, including inorganic salts and organic bases, on the stability of these MOFs is examined. The destruction of the framework is confirmed through powder X-ray diffraction (PXRD) patterns, and the monitored dissolution of ligands from the framework is assessed using nuclear magnetic resonance (NMR) spectroscopy. Our key findings reveal a direct correlation between the strength and concentration of the base and the destruction of the MOFs. The summarized data provide valuable insights that can guide the practical application of Zr-based UiO-66 MOFs under basic conditions, offering essential information for their optimal utilization in various settings.

Nickel Catalyzed Vinylidene Insertions into O-H Bonds.

A (pybox)Ni catalyst (pybox = pyridine-bis(oxazoline)) promotes the reductive cyclization of ß-hydroxy 1,1-dichloroalkenes to form 2,3-dihydrofurans. The substrates for this reaction are conveniently prepared by an aldol addition followed by one-carbon homologation. Chiral substrates are accessible in highly enantioenriched form, allowing for the synthesis of stereochemically complex 2,3,4-trisubstituted products. Mechanistic studies support a vinylidene O-H insertion pathway rather than C-O cross-coupling followed by reductive dechlorination.

TEMPO-radical-bearing metal-organic frameworks and covalent organic frameworks for catalytic applications.

It is known that 2,2,6,6-tetramethylpiperidinyl-1-oxy (or TEMPO) is a stable, radical-containing molecule, which has been utilized in various areas of organic synthesis, catalysis, polymer chemistry, electrochemical reactions, and materials chemistry. Its unique stability, attributable to its structural features, and molecular tunability allows for the modification of various materials, including the heterogenization of solid materials. Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are porous and tunable because of their ligand or linker portion, and both have been extensively studied for use in catalytic applications. Therefore, synergistically combining the chemistry of TEMPO with the properties of MOFs and COFs is a natural choice and should allow for significant advancements, including improved recyclability and selectivity. This article focuses on TEMPO-bearing MOFs and COFs for use in catalytic applications. In addition, recent strategies related to the use of these functional porous materials in catalytic reactions are also discussed.

Oxidative Coupling of 3-Oxindoles with Indoles and Arenes.

A highly efficient method for the oxidative coupling of 2-substituted 3-oxindoles with aromatic compounds to form 2,2-disubstituted indolin-3-ones with broad scope is described. This work utilized oxygen as the terminal oxidant and a base-metal catalyst under mild conditions instead of toxic/precious-metal reagents and higher-molecular-weight oxidants. Quaternary structures were produced in modest-to-excellent yields (up to 96 %) without prefunctionalization.

Total Synthesis of Chaetoglobin A via Catalytic, Atroposelective Oxidative Phenol Coupling.

The first total synthesis of chaetoglobin A (1), which features a chiral axis between two identical highly oxygenated bicyclic cores, was successfully completed in 12 steps from 2,6-dimethoxytoluene. Vanadium-catalyzed oxidative phenol coupling, as a key step, enabled generation of the axial chirality.

Asymmetric Oxidative Coupling of Phenols and Hydroxycarbazoles.

The first examples of asymmetric oxidative coupling of simple phenols and 2-hydroxycarbazoles are outlined. Generation of a more vanadium catalyst by ligand design and by addition of an exogenous Brønsted or Lewis acid was found to be key to coupling the more oxidatively resistant phenols. The resultant vanadium complex is both more Lewis acidic and more strongly oxidizing. Good to excellent levels of enantioselectivity could be obtained, and simple trituration readily provided the products with ≥95% ee.

ß-Silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone for the total synthesis of (±)-pancratistatin.

A new synthetic route to (±)-pancratistatin was devised utilizing ß-silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone. The TMS group incorporated in the cycloadduct permitted a facile elimination process for the eventual installation of the C(1)-OH function. Subsequent transformations including Curtius rearrangement and Bischler-Napieralski reactions completed the total synthesis of (±)-pancratistatin.

Total synthesis of (+/-)-galanthamine via a C3-selective Stille coupling and IMDA cycloaddition cascade of 3,5-dibromo-2-pyrone.

A new efficient synthetic route to (+/-)-galanthamine was devised by using a tandem C3-selective Stille coupling-IMDA cascade of 3,5-dibromo-2-pyrone as a key strategy.