Organic Chemistry Frontiers最新文献

The field of nucleophilic organocatalysis has garnered enormous interest and utility in the past two decades. Additionally, radical chemistry, mainly driven by the research progress in photocatalysis and electrocatalysis, has regained extensive attention. The unique reactivity of free radicals, which is different that of from closed-shell species, provides a solution to issues in electron-pair-mechanism-based catalysis. In this review, we highlight the advances in single-electron nucleophilic organocatalysis. We have separated the review into amine, N-heterocyclic carbene (NHC) and phosphine sections according to the type of organocatalyst. The strategies for the generation of radical species and the formation of new bonds are emphasized in the discussions of specific reactions. The final section provides a brief outline of the relationships among different nucleophilic organocatalysis and the prospects for future development.

Internally substituted π-systems have remained somewhat underexplored in contrast to their peripherally functionalized counterparts. In this study, we compare a bowl-shaped aromatic hydrocarbon with internal methoxy groups to related derivatives with hydrogen, methyl, and anisyl groups, evaluating their electron-accepting properties, electronic absorption spectra, and fullerene-binding behavior. The methoxy-substituted derivative exhibits enhanced electron-accepting properties and positively shifted electrostatic potential mapping on its concave surface due to the inductive effect of the oxygen atoms. The σ* orbitals of the internal C–O bonds participate in π-conjugation to change the absorption properties of the bowl-shaped π-skeleton. As hydrocarbons internally substituted with oxygen are key fragments of graphene oxide, these results can be expected to aid the understanding of the structure–property relationships in graphene oxide. Furthermore, internal substitution with oxygen atoms decreases the efficiency of fullerene-binding, thus affording fundamental insights into the design of advanced fullerene-receptors.

Novel cyclic fluorinated sulfoximines featuring an E-monofluoroalkenyl benzoisothiazole 1-oxide moiety as single diastereomers can be facilely accessed by Rh(III)-catalyzed redox-neutral [4 + 1] annulation of sulfoximines with α,α-difluoromethylene alkynes. The reaction proceeds with sequential selective cleavage of both C–H and C–F bonds, thus exhibiting high step and atom economy. Through a combined experimental and computational mechanistic study, the origins of annulative chemoselectivity, unconventional E-selectivity, and excellent diastereoselectivity have been revealed accordingly.

Hermaphroditism of molecules: as in nature some species behave as male or female depending on the environment, herein we report a bispericyclic dimerisation of cyclic 1-azadienes where a molecule can behave as either diene or dienophile, depending on its location at the transition state. In a symmetrical reactive complex, here represented by an arbitrary reference system, a molecule that is positioned on top acts as the diene unit, while the dienophile partner is the one situated at the bottom. In addition, a strong chiral self-recognition phenomenon is observed, where each enantiomer within a racemic mixture of chiral 1-azadienes exclusively recognises itself. In order to shed some light into the understanding of the chiral self-recognition effect, an extensive DFT study of the reaction pathway is provided, concluding that a combination of attractive π-stacking forces and repulsive steric interactions is at the origin of the high stereospecificity of the reaction.

This study introduces a cascade approach for synthesizing functionalized (2-furyl)-2-pyrrolidines, showcasing both convergence and remarkable stereoselectivity. This domino process proceeds through an N–H insertion into an enynal-derived metal–carbenoid, followed by an intramolecular aldol reaction to provide pyrrolidines with high diastereoselectivity (98 : 2). This chemistry utilizes Earth-abundant zinc chloride as a catalyst with loading as low as 1 mol%. This method operates under mild conditions and demonstrates high chemoselectivity by accommodating substrates bearing functionalities such as free alcohols, alkenes, and alkynes.

The reactivities of both diastereomers of hexabenzotriphenylene (HBTP), a triple carbo[5]helicene of the formula C₄₂H₂₄, were examined in the presence of phenyliodine diacetate (PIDA) as an oxidizing agent. The D₃-symmetric diastereomer afforded two different ring rearranged ketone-containing products embedding a spirofluorene moiety. In contrast, under similar conditions, the C₂-symmetric diastereomer afforded predominantly a cyclodehydrogenation product. Altogether, this shows that stereochemistry is a critical factor in the reactivity of non-planar polycyclic aromatic hydrocarbons.

In this paper, we report a photochemical strategy for the visible light-mediated efficient conversion of (2-vinylaryl)methanol derivatives to the corresponding aryl aldehydes or aryl ketones in moderate to excellent yields with broad substrate scope under mild conditions. This photochemical process takes place from the generation of the triplet state of olefins and involves 1,5-hydrogen atom transfer, enol tautomerization, and a subsequent proton transfer process. The plausible reaction mechanism has been verified by deuterium labeling and control experiments, kinetic and Stern–Volmer analyses, and DFT calculations.

The cascade [4 + 2] annulation/aromatization reactions between carbodiimide anions and α,β-unsaturated imines are developed. This is the first report on regulating N-Ts cyanamides to participate in reactions absolutely via carbodiimide anions rather than previously reported cyanamide anions, affording a convenient method for synthesizing 2-aminopyrimidines. More importantly, this work expands the application of carbodiimides, broadening the coupling substrate scope to electrophilic partners and providing new strategies to construct six-membered N-heteroaromatic scaffolds. A stepwise mechanism, supported by DFT calculations, is invoked to explain the reaction selectivity.

Catalysis by small organic molecules capable of binding and activating substrates through attractive, non-covalent interactions has emerged as a highly significant approach in the fields of organic and organometallic chemistry. Notably, the utilization of organo-chalconium catalysts has gained substantial attention, owing to their remarkable catalytic properties, within the realms of synthetic chemistry and small molecule catalysis. In this study, we present a direct C2,3–H difunctionalization of indoles with unactivated amines (secondary aliphatic amines, more than 66 examples, up to 95% isolated yield), facilitated by the organo-chalconium catalyst generated through the reaction of iodine and chalconium reagents. This exceptional strategy not only provides a formidable tool for the assembly of intricate molecular architectures, but also affords the ability to perform late-stage functionalization of natural products and pharmaceutical compounds. Moreover, this advancement imparts unparalleled potential for optimizing the bioactivity and pharmacokinetic properties of existing drugs.

Herein, a formal highly enantioselective organocatalyzed [3 + 2] cycloaddition of furanone derivatives and azomethine ylides is presented. The success of this reaction resides in intramolecular hydrogen bond activation through an o-hydroxy group at the aromatic ring of the imine, allowing the formation of highly multifunctional bicyclic adducts with five stereogenic centers in a stereocontrolled manner. Furthermore, the reaction is paired with a highly efficient kinetic resolution of butenolides, achieving selectivity factors above 200. Using this methodology, furan-2(5H)-ones and furo[3,4-c]pyrrolidinones were obtained with high enantioselectivities. Quantum chemistry calculations reveal the crucial role of the hydrogen bond formed between the catalyst donor-units and the two reactants, which modifies their arrangement and promotes effective facial discrimination resulting in a highly selective kinetic resolution. In addition, further applicability of the kinetic resolution process is shown.