Regiodivergent catalytic asymmetric dearomative cycloaddition of bicyclic heteroaromatics

Visible light-driven dearomative meta-cycloadditions of 2-acetonaphthalenes via triplet energy transfer cascade

Dearomative cycloadditions (DACs) with ortho- and para-variants have been well documented under visible light-mediated triplet-triplet energy transfer (VLEnT) catalysis. The prospective [3 + 2] or the meta-DACs propelled via VLEnT catalysis remains elusive. Classically, meta-DACs are known under harsher UV irradiations and are symmetry allowed in the excited singlet potential energy surface. Herein, we report formal meta-DACs of 2-acetonaphthalenes propagated via a two-step VLEnT cascade circumventing the attainment of energetically higher singlet excited states. The photosensitizer selectively promotes the [4 + 2] cycloaddition followed by a contra-thermodynamic di-π-methane type skeleton rearrangement cascade. The DFT studies in conjugation with electrochemical, photoluminescence, kinetic, quadratic dependency, and control experiments support the VLEnT cascade. The described protocol delivers highly sp3-rich polycyclic frameworks in high yields with wide functional group tolerance. The inclusion of bioactive molecules and the establishment of a wide array of post-synthetic derivatizations further underscores the adaptability of the methodology for generating complex three-dimensional molecules.

Regioselective Aryne Annulations of N-Tosyl-2-enamides and N-tert-Butylsulfinyl-2-enamides for the Construction of Dihydroquinolin-4-one and Chroman-4-imine Units

A regioselective synthesis of the dihydroquinolin-4-one 4 is achieved from the aryne-mediated annulation of an o-(trimethylsilyl)aryl triflate 1 with N-tosyl-2-enamide 2 in the presence of TBAT in toluene, whereas the chroman-4-imine 5 is formed from the reaction of 1 with N-(tert-butylsulfinyl)-2-enamide 3 and TBAF in THF. Governing factors for regioselectivity have been accounted for as strong steric and electronic effects between N-toluenesulfonyl and N-tert-butylsulfinyl groups in 2 and 3. The methods described herein are successful with various substrates 1 with 2 or 3 in high levels of regioselectivity, and diastereoselectivity for 5.

Bioactive atropisomers: Unraveling design strategies and synthetic routes for drug discovery

Atropisomerism, an expression of axial chirality caused by limited bond rotation, is a prominent aspect within the field of medicinal chemistry. It has been shown that atropisomers of a wide range of compounds, including established FDA-approved drugs and experimental molecules, display markedly different biological activities. The time-dependent reversal of chirality in atropisomers poses complexity and obstacles in the process of drug discovery and development. Nonetheless, recent progress in understanding atropisomerism and enhanced characterization methods have greatly assisted medicinal chemists in the effective development of atropisomeric drug molecules. This article provides a comprehensive review of their special design thoughts, synthetic routes, and biological activities, serving as a reference for the synthesis and biological evaluation of bioactive atropisomers in the future.

Controlling Diastereoselectivity in Dearomatizing Diels-Alder Reactions of Nitroarenes with 2-Trimethylsilyloxycyclohexadiene

Dearomative Diels-Alder cycloadditions between nitroarenes and 2-trimethylsilyloxycyclohexadiene are carried out under high pressure at room temperature in the absence of any chemical promoter. Reactions are performed with different arenes, including the highly aromatic naphthalenes and quinolines. They lead to 3D-scaffolds with exquisite exo-diastereoselectivity. The exo approach is characterized by lower distortion of the substrates in a late TS and by more favorable orbital interactions presumably between the nitro group and the dienic part, explaining the stereoselectivity.

Catalytic Atroposelective Synthesis of Axially Chiral Azomethine Imines and Neuroprotective Activity Evaluation

Azomethine imines, as a prominent class of 1,3-dipolar species, hold great significance and potential in organic and medicinal chemistry. However, the reported synthesis of centrally chiral azomethine imines relies on kinetic resolution, and the construction of axially chiral azomethine imines remains unexplored. Herein, we present the synthesis of axially chiral azomethine imines through copper- or chiral phosphoric acid catalyzed ring-closure reactions of N'-(2-alkynylbenzylidene)hydrazides, showcasing high efficiency, mild conditions, broad substrate scope, and excellent enantioselectivity. Furthermore, the biological evaluation revealed that the synthesized axially chiral azomethine imines effectively protect dorsal root ganglia (DRG) neurons by inhibiting apoptosis induced by oxaliplatin, offering a promising therapeutic approach for chemotherapy-induced peripheral neuropathy (CIPN). Remarkably, the (S)- and (R)-atropisomers displayed distinct neuroprotective activities, underscoring the significance of axial stereochemistry.

A Regioselective [3 + 2] Cycloaddition of Alkynols and Ketones To Access Diverse 1,3-Dioxolane Scaffolds

This study presents a stepwise exoselective [3 + 2] cycloaddition reaction of alkynols with ketones, leading to the synthesis of 4-methylene-1,3-dioxolane derivatives. Remarkably, without any Thorpe-Ingold induced effect, the cyclization reaction was demonstrated with complete regio- and chemoselectivity, which was solely promoted by cesium carbonate. A wide range of unactivated ketones are viable under these mild reaction conditions, and both primary and tertiary alkynols are compatible with these cyclization reactions. We have prepared a diverse array of highly dense exomethylene 1,3-dioxolane rings demonstrating a remarkable tolerance for various functional groups.