Organic chemistry frontiers : an international journal of organic chemistry最新文献

The synthesis of chiral α-amino acid derived (1,2,3-triazol-4-yl)-picolinamide (tzpa) ligands 4–6 designed by combining the coordination properties of two well-known ligand structures within a single unit is described. The self-assembly formation between these ligands and the lanthanide ion Tb(iii) was investigated in solution by probing the ground and the singlet excited state properties of the ligands as well as monitoring the evolution of the Tb(iii) emission at long wavelengths. The spectroscopic results showed that while under thermodynamic control the 1 : 3 (Tb : L) is produced, then analysis of the titration data using non-liner regression analysis demonstrated that the main species in solution is the 1 : 2 (Tb : L) after the addition of 0.5 equivalents of Tb(iii).

Regioselective functionalization of C–H bonds has attracted the attention of chemists in recent years. However, transition metals are often expensive and indispensable in most C–H activation reactions. Here, we describe a metal-free intramolecular heteroarene C(sp²)–H amination from unprotected (hetero)arylamines. Exposure of 2-(pyridin-3-yl)aniline to potassium tert-butoxide was found to access N-heterocycles without additives, which unlocks a new breakthrough. This process is involved in the synthesis of a wide variety of N-heterocycles including natural products and bioactive compounds. Mechanistic studies have established that these reactions proceed through an S_NArH process. Such a unique transformation opens the door toward the regioselective intramolecular C–H amination of weakly reactive arylamines with heterocyclic compounds.

We report here a facile and efficient vinylation method using Fe-catalyzed cross-electrophile coupling of readily available vinyl- and hydro-chlorosilanes with a variety of substituted alkenyl bromides using manganese as the terminal reductant. This C(sp²)–Si forming modular approach shows excellent functional group tolerance and broad substrate scope, which allows the creation of a series of vinyl organosilanes, including electron-rich, electron-poor, and ortho-/meta-/para-substituted vinyl electrophiles, which were coupled successfully. Moreover, several substrates with structurally complex natural products and pharmaceutical motifs were well modified by this vinyl silylation process. Gram-scale reaction and derivatization of the formed vinyl organosilanes are demonstrated.

Carboranes, a class of carbon–boron molecular clusters, have unique characteristics and are finding a variety of applications ranging from materials to medicine. In this connection, selective functionalization of o-carboranes has attracted enormous research interest, particularly in regio- and enantio-selective cage B–H derivatization among ten chemically similar BH vertices in o-carboranes. Over the years, precious transition metal-catalyzed cage B–H functionalization has made significant advances in the preparation of diversely functionalized o-carboranes. In contrast, research on B–H functionalization via a base metal catalysis strategy has just begun recently. This paper summarizes the recent developments in base metal-catalyzed regioselective B–H functionalization of carboranes.

Compounds bearing oxa-quaternary carbon centers, such as chiral tertiary alcohols, ethers, esters, and acetals, are widely found in a number of bioactive compounds, natural products, agrochemicals and drugs. Besides, they could also serve as privileged building blocks in organic synthesis, especially in a series of bond-forming transformations. Alternatively, among these compounds, enantiomerically pure tertiary alcohols have been extensively used to develop new chiral ligands for a range of organic transformations based on their inherent rigidity and bulky three-dimensional environment. Therefore, developing efficient strategies for the enantioselective catalytic synthesis of these compounds has been of long-standing interest among the chemical and pharmaceutical communities for decades. In contrast to chiral oxa-tertiary stereocenters, the construction of enantioenriched oxa-quaternary carbon centers remains a great challenge in asymmetric synthesis due to the less reactive nature of their precursors and the decreased enantioface differentiation between the two substituents at the prochiral carbon center. Although several tutorial reviews on the asymmetric synthesis of chiral compounds bearing quaternary stereocenters have appeared, there is no specialized review that summarizes the content of enantioselective construction of oxa-quaternary stereocenters. Due to the rapid development in this research field, a timely summarization of the recent achievements is highly valuable. This review exclusively focuses on the recent advances (from 2020 to the beginning of 2023) in asymmetric reactions for the synthesis of enantiomerically pure compounds bearing oxa-quaternary stereocenters.

Enantioselective formal (3 + 2) cyclization of cyclic β-keto esters with azonaphthalenes has been established. A range of cyclopenta[b]indoles have been synthesized in good yields (up to 99% yield) with high diastereo- and enantioselectivity (up to 96% ee, >19 : 1 dr) by using guanidine-amides as catalysts under mild reaction conditions. A bifunctional hydrogen-bond activation model was rationalized for the origin of enantioselectivity.

Dirhodiums, which feature lantern- or paddlewheel-like structures, have emerged as a class of useful catalysts in organic synthesis. Among the transformations catalyzed by dirhodiums, the carbene, with diazo, cyclopropene, hydrazone and triazole as the precursors, and nitrene transfer reactions are dominant and have reached remarkable levels of efficiency and selectivity. Additionally, more and more fascinating properties of dirhodium have been explored and discovered in the past few decades, which has accelerated the applications of dirhodium in organic synthesis. In this review, we aim to showcase these advances in dirhodium-catalyzed transformations. The transformations including cycloisomerization, hetero-Diels–Alder (HDA) reactions, ene reactions, arylation, radical oxidation reactions and C–H activation, etc. will be covered. In these reactions, the dirhodiums could not only work as redox-neutral catalysts but also as redox catalysts.

Glycosidases play important roles in modulating the structural and functional integrity of glycoproteins and glycolipids, and thus are promising biomarkers for disease diagnosis. While current approaches for glycosidase detection mainly rely on an enhancement of the UV-vis absorbance or fluorescence emission of glycosyl indicators, here we develop a ratiometric fluorescent probe for the sensitive and selective detection of glycosidase activity based on the combined mechanisms of excited-state intramolecular proton transfer (ESIPT) and solid-state luminescence enhancement (SSLE). The probe behaves like a typical SSLE when glycosylated, and exhibits a ∼140 nm red-shift in fluorescence owing to activation of ESIPT after deglycosylation. Such a large Stokes shift may facilitate the unbiased analysis of glycosidase activities when used in diagnostic and drug-screening assays.

A facile approach for quick and efficient access to structurally complex 2,3-naphthalimide derivatives is developed. Easily accessible and inexpensive β-arylpropiolic acids and primary amines are used as the reaction starting materials. Both reactants can tolerate a diversity of substituents with various electronic and steric effects. Multi-functional 1-aryl-2,3-naphthalimides are afforded in generally moderate to excellent yields through a consecutive cascade amidation/dehydro-Diels–Alder reaction in one-pot operations. Promising applications of the afforded 1-aryl-2,3-naphthalimide products in bactericide development for plant protections are also exhibited.

A photocatalyzed regioselective alkoxycarbonylmethylation of 2-aminopyridines with α-diazoacetates has been developed. This method provides a metal-free strategy to assemble 2-aryl-2-pyridylacetic esters via a direct pyridyl Csp²–H bond carbenoid insertion under mild conditions.