Organic & Biomolecular Chemistry最新文献

Herein, a novel cascade cyclization for the synthesis of oxyalkylated and 1,5-dicarbonylated chroman-4-ones from 2-(allyloxy)arylaldehydes is described. The transformation proceeded in the presence of a silver salt to generate a series of anticipated chroman-4-one derivatives in moderate to good yields, and the alcohols or ketones in this reaction were employed as both reaction media and oxyalkyl or carbonyl sources, exhibiting an atom-economical approach for the preparation of chroman-4-one skeletons.

An iridium(III) complex bearing a picolinamidato ligand has been developed as an efficient catalyst for the regioselective C3 alkylation of indoles and oxindoles via a borrowing hydrogen (BH) or hydrogen autotransfer strategy. A broad range of aromatic, heteroaromatic, and aliphatic alcohols, including diols, are successfully employed under solvent-free (neat) conditions with low catalyst loading, demonstrating excellent functional group tolerance. Significantly, this protocol combines high regioselectivity, atom economy, and operational simplicity by avoiding preactivated alkylating agents, external oxidants, or reductants, thereby advancing sustainable C-C bond-forming methodologies. The method is scalable and provides straightforward access to structurally diverse and biologically relevant indole and oxindole frameworks, which are prevalent motifs in pharmaceuticals and natural products. Control experiments, deuterium labeling studies, and spectroscopic investigations support a classical borrowing hydrogen mechanism involving Ir-hydride intermediates.

With the assistance of a chiral phosphine catalyst, a remote-controlled enantioselective (3 + 2)-annulation between pyrrolidinone-based Morita-Baylis-Hillman (MBH) carbonates and 2-arylideneindane-1,3-diones has been successfully realized under mild conditions. This reaction efficiently constructs chiral (spiro[cyclopenta[b]pyrrole-6,2'-inden]-3-yl)acrylates with high efficiency and enantioselectivity. Notably, the asymmetric transformation proceeds through the selective activation of the C^ε and C^ε' positions of the pyrrolidinone-based MBH carbonates.

Herein, we present a novel and environmentally friendly method for synthesizing carbazoles relying on palladium catalysis in water as a green reaction medium. The process utilizes surfactant-associated palladium nanoparticles (PdNPs) with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) for aryl C-H activation of 2-halo-N-arylanilines under microwave irradiation. There, DBU as a base and ligand enhances the efficiency of the Pd-nanocatalyst. The mild method offers excellent chemoselectivity for the C-I bond over other carbon-halogen bonds, and functional group compatibility, enabling the synthesis of forty-three carbazoles, including three bioactive natural alkaloids - glycozoline, clausine L, and clausine H - with up to 99% yields. Here, micelles of the cationic surfactant in water are found to be beneficial for stabilizing the PdNPs, facilitating their recycling and probably limiting the C-Pd protolysis. A simple experimental setup for Pd-catalyzed aryl C-H activation in water, under ambient conditions, use of inexpensive innocuous additives, and avoidance of elaborate phosphine or N-heterocyclic carbene ligands are the obvious features of this approach. Besides being environmentally benign, the present report on Pd/DBU catalysis in water provides a simple procedure and rapid access to diversely functionalized carbazoles.

Thiazolidine- and oxazolidine-4-carboxylates derived from L-cysteine and L-serine, respectively, as well as their structural analogues with different substitution patterns at the 1,3-heterocycle, were prepared and evaluated as hydrolytically cleavable profragrances for practical applications in functional perfumery. Hydrolysis experiments at acidic and alkaline pH and dynamic headspace measurements on cotton in a typical fabric softener or liquid detergent application showed that oxazolidine-4-carboxylates rapidly hydrolysed, whereas thiazolidine-4-carboxylates were sufficiently stable to successfully release fragrances from the target surface over several days. Substitution of the heterocycle at the N-atom or at the 5-position had a strong impact on fragrance release and on side reactions, such as ester hydrolysis at alkaline pH. The compounds did not form rapidly equilibrating reversible systems in aqueous media. Unsubstituted thiazolidine-4-carboxylates successfully released fragrances from acidic and alkaline product formulations, which is unusual for hydrolytically labile pH-dependent delivery systems. They provided a long-lasting fragrance effect in the two laundry care applications tested and thus represent a simple and straightforward, universally applicable solution for efficient fragrance delivery under realistic everyday life conditions.

A highly efficient method for the terminal iodination of alkynes is developed to access multi-functionalized alkynes containing an iodo and a propargyl ether group under mild reaction conditions using an I₂/K₂CO₃ system in methanol. Reactions enable the synthesis of 1,2-diiodoalkenes containing an allyl ether via diiodination using the I₂/KI reagent system in water under ultrasonication. Chemoselectivity has been achieved by a judicious choice of the reaction conditions for synthesizing monoiodination and diiodination products. This diversity-oriented synthesis requires no purification, allowing access to a variety of compounds in pure forms in excellent yields. The reactions are compatible with many substrates, and practical applications are demonstrated with a scale-up reaction.

A series of photoreversible anion binding hosts is developed, combining either an azobenzene or an arylazopyrazole as a central photoswitch unit and tetrakis-triazoles as anion binding motifs. By broad structural variations, including different linker types and positions between the triazoles, the anion binding contrast of both isomers is maximized, with the Z isomer exhibiting a binding constant of up to a factor of 16 larger than that of the E isomer. Back-isomerisation Z → E is studied with respect to the influence of a bound anion. Anion binding stabilizes the Z-isomer against thermal isomerization, providing a two-fold lifetime of the Z isomer. A reduced photoisomerization rate and an enhanced Z/E ratio in the photostationary state correlate with the anion binding constant of the Z isomer, which is probably due to the modified photophysical processes.

A major goal in modern synthetic chemistry is to develop sustainable and cost-efficient methodologies for the synthesis of complex, chiral molecules-particularly those with pharmaceutical importance. In this context, there are different types of approaches being used for the sustainable synthesis of organic molecules, including biocatalysis, electrosynthesis, and photocatalysis. Enzymes, or biocatalysts, are integral to synthetic chemistry, offering exceptional chemo-, regio-, and enantioselectivity while operating under mild and environmentally benign conditions. Despite these advantages, their application is often limited by narrow substrate scope and restricted reactivity. To overcome these limitations, one promising approach is to integrate biocatalysis with other catalytic techniques. These integrated strategies offer new opportunities for selective and green synthesis. However, a significant challenge lies in the potential deactivation of enzymes when used alongside other catalysts, which can compromise the overall catalytic efficiency. To address this challenge, it is essential to identify reaction conditions that preserve the stability and activity of each catalytic component. Achieving such compatibility is key to enabling efficient multi-catalytic cascade processes for the synthesis of drug-like compounds. This review highlights recent progress, particularly over the last six years, in the field of hydrolase-catalyzed reactions integrated with chemical, electro-, and photocatalysis, emphasizing their emerging role in advanced synthetic methodologies.

Asymmetric inverse-electron-demand cycloaddition reactions of cyclic nitrones with o-hydroxystyrenes have been developed using a quinine-derived chiral amine-urea. The high levels of asymmetric induction are found to be afforded by an Anti-Open-S mechanism involving a dual activation system.

We report a palladium-catalyzed esterification reaction involving difluoroallyl bromides. This synthetic strategy involves the activation of fluorinated bromohydrocarbons by palladium catalysis and a direct C–O coupling reaction with a weakly nucleophilic indole carboxylic acid to obtain indole carboxylic esters. The key of this reaction lies in the selective coordination and activation of 3-bromo-3,3-difluoropropene by the palladium catalyst. The reaction overcomes the influence of the unique electronic effects of the difluoromethylene group on alkene reactivity, directly establishing an efficient new method for the synthesis of difluoroallyl esters, while exhibiting good substrate compatibility and moderate functional group tolerance. It not only applies to indole-based substrates but also can convert pyrrole/aromatic acids into the corresponding carboxylic esters. Overall, this study provides a practic al and straightforward synthetic approach for difluoroallyl-substituted indole/pyrrole/aromatic carboxylic esters.