Iridium-catalyzed direct asymmetric reductive amination utilizing primary alkyl amines as the N-sources

Electrophilicity Modulation for Sub-ppm Visualization and Discrimination of EDA

Precise and timely recognition of hazardous chemical substances is of great significance for safeguarding human health, ecological environment, public security, etc., especially crucial for adopting appropriate disposition measures. Up to now, there remains a practical challenge to sensitively detect and differentiate organic amines with similar chemical structures with intuitive analysis outcomes. Here, a unique optical probe with two electrophilic recognition sites for rapid and ultra-sensitive ratiometric fluorescence detection of ethylenediamine (EDA) is presented, while producing distinct fluorescence signals to its structural analog. The probe exhibits ppb/nmol level sensitivity to liquidous and gaseous EDA, specific recognition toward EDA without disturbance to up to 28 potential interferents, as well as rapid fluorescence response within 0.2 s. By further combining the portable sensing chip with the convolutional algorithm endowed with image processing, this work cracked the problem of precisely discriminating the target and non-targets at extremely low concentrations.

Chiral Discrimination of Acyclic Secondary Amines by 19F NMR

Chiral aliphatic amine compounds exhibit a range of physiological activities, making them highly sought-after in the pharmaceutical industry and biological research. One notable obstacle in studying these compounds stems from the pronounced steric hindrance surrounding the nitrogen atom. This characteristic often leads to a weak affinity of acyclic secondary amines for molecular probes, making their chiral discrimination intricate. In response to this challenge, our research has unveiled a novel 19F-labeled probe adept at recognizing and distinguishing between enantiomers of these acyclic secondary amines. By strategically incorporating a single fluorine atom as the 19F label, we have managed to diminish the steric hindrance at the binding site. This alteration bolsters the probe's affinity toward bulkier analytes. As a testament to its effectiveness, we have successfully employed our probe in the chiral analysis of relevant pharmaceuticals, accurately determining their enantiocomposition.

An Asymmetric Hydrogenation/N-Alkylation Sequence for a Step-Economical Route to Indolizidines and Quinolizidines

The direct catalytic asymmetric hydrogenation of pyridines for the synthesis of piperidines remains a challenge. Herein, we report a one-pot asymmetric hydrogenation of pyridines with subsequent N-alkylation using a traceless Brønsted acid activation strategy. Catalyzed by an iridium-BINAP complex, the substrates undergo ketone reduction, cyclization and pyridine hydrogenation in sequence to form indolizidines and quinolizidines. The absolute configuration of the stereocenter of the alcohol is retained and influences the formation of the second stereocenter. Experimental and theoretical mechanistic studies reveal that the chloride anion and certain noncovalent interactions govern the stereoselectivity of the cascade reaction throughout the catalytic process.

Diastereoselective Reductive Etherification Via High-Throughput Experimentation: Access to Pharmaceutically Relevant Alkyl Ethers

This manuscript describes the development of the first diastereoselective intermolecular synthesis of alkyl ethers via reductive etherification of diverse ketones or aldehydes with alcohols. Key to this development was the use of low-temperature high-throughput experimentation (HTE) technologies that enabled rapid reaction optimizations and parallel synthesis. A broad scope of pharmaceutically relevant substrates was surveyed, which formed alkyl ethers effectively. In addition, we demonstrated that the diastereoselectivity of this transformation can be readily modulated by prudent selection of the reductant.

Ru-Catalyzed Direct Asymmetric Reductive Amination of Bio-Based Levulinic Acid and Ester for the Synthesis of Chiral Pyrrolidinone

Direct asymmetric reductive amination of bio-based levulinic acid (LA) to the enantioenriched 5-methylpyrrolidinone is achieved by using a readily available chiral Ru/bisphosphine catalyst with excellent enantioselectivity (up to 96 % ee) and high isolated yield (up to 89 %). Methyl levulinate (ML), a byproduct from the industrial production of 2,5-furandicarboxylic acid (FDCA), can be used instead of LA with similar reactivity and selectivity. Mass spectrometry and isotope labelling studies indicate that the chiral lactam is formed via imine-enamine tautomerization/cyclization followed by asymmetric hydrogenation of the cyclic enamide.

Chiral 8-Amino-5,6,7,8-tetrahydroquinoline Derivatives in Metal Catalysts for the Asymmetric Transfer Hydrogenation of 1-Aryl Substituted-3,4-dihydroisoquinolines as Alkaloids Precursors

Chiral diamines based on an 8-amino-5,6,7,8-tetrahydroquinoline backbone, known as CAMPY (L1), or the 2-methyl substituted analogue Me-CAMPY (L2) were employed as novel ligands in Cp* metal complexes for the ATH of a series of substituted dihydroisoquinolines (DHIQs), known for being key intermediates in the synthesis of biologically active alkaloids. Different metal-based complexes were evaluated in this kind of reaction, rhodium catalysts, C3 and C4, proving most effective both in terms of reactivity and enantioselectivity. Although modest enantiomeric excess values were obtained (up to 69% ee in the case of substrate I), a satisfactory quantitative conversion was successfully fulfilled even in the case of the most demanding hindered substrates when La(OTf)₃ was used as beneficial additive, opening up the possibility for a rational design of novel chiral catalysts alternatives to the Noyori-Ikariya (arene)Ru(II)/TsDPEN catalyst.