A simple and convergent synthetic strategy used to increase the diversity of the carbodicarbene ligand framework through incorporation of unsymmetrical pendant groups is reported. Structural analysis ...and spectroscopic studies of ligands and their Rh complexes are reported. Reactivity studies reveal carbodicarbenes as competent organocatalysts for amine methylation using CO2 as a synthon. A unique BH‐activated boron–carbodicarbene complex was isolated as a reaction intermediate, providing mechanistic insight into the CO2 functionalization process.
Expanding the family: A simple and convergent synthetic strategy was developed to increase the diversity of the carbodicarbene ligand framework by incorporation of unsymmetrical pendant groups. Reactivity studies revealed that carbodicarbenes are competent organocatalysts for amine methylation using CO2 as a synthon.
Development of photocatalysts (PCs) with diverse properties has been essential in the advancement of organocatalyzed atom transfer radical polymerization (O‐ATRP). Dimethyl dihydroacridines are ...presented here as a new family of organic PCs, for the first time enabling controlled polymerization of challenging acrylate monomers by O‐ATRP. Structure–property relationships for seven PCs are established, demonstrating tunable photochemical and electrochemical properties, and accessing a strongly oxidizing 2PC.+ intermediate for efficient deactivation. In O‐ATRP, the combination of PC, implementation of continuous‐flow reactors, and promotion of deactivation through addition of LiBr are critical to producing well‐defined acrylate polymers with dispersities as low as 1.12. The utility of this approach is established through demonstration of the oxygen‐tolerance of the system and application to diverse acrylate monomers, including the synthesis of well‐defined di‐ and triblock copolymers.
Polymers in flow: Organic photoredox catalysis is applied to the controlled synthesis of poly(acrylates). This advancement is enabled by the development of new organic photoredox catalysts, dimethyl dihydroacridines, with unique properties. The use of continuous flow reactors is also key to the success of the method.
A novel NHC‐catalyzed annulation protocol for the asymmetric synthesis of biologically important β‐lactam fused spirocyclopentane oxindoles with four contiguous stereocenters, including two ...quaternary carbon centers, was developed. Alternatively, spirocyclopentane oxindoles containing an enaminone moiety can be achieved using the same starting materials, isatin‐derived enals, and N‐sulfonyl ketimines, in the presence of a slightly different NHC catalytic system. This switchable annulation strategy enables the selective assembly of both heterocyclic scaffolds with good yields and excellent enantioselectivities for a broad range of substrates.
Flip a switch: The switchable NHC‐catalyzed asymmetric reaction between isatin‐derived enals and N‐sulfonyl ketimines by the homoenolate pathway selectively leads to spirocyclopentane oxindoles bearing either a β‐lactam or an enaminone moiety. The reaction proceeds in high yields and with excellent stereoselectivities for a wide range of substrates.
The twinkling of an I: In a new atom‐economical and environmentally friendly organocatalytic method for intramolecular CH amination, the CN bond forms at ambient temperature by ion of two atoms of ...hydrogen; only acetic acid and water are formed as by‐products. The method has also been extended to the unprecedented metal‐free cross‐amination of nonactivated arenes.
The surface initiated ring opening polymerization (SI-ROP) of cellulose nanofibers (CNF) with rac-Lactide under mild conditions using N,N-dimethyl aminopyridine (DMAP) was investigated. The influence ...of catalyst amount, monomer-to-initiator (cellulose surface –OH groups) ratio, temperature, and cellulose preconditioning (lyophilization vs solvent exchange) were studied to determine the best SI-ROP conditions, and to understand the effect of the parameters on grafting efficiency. The fibers modified after lyophilization had a PLA content comparable to those obtained with traditional metal catalysts (e.g. tin-(II)ethylhexanoate). Starting from a stable dispersion of CNF in dichloromethane obtained through solvent-exchange showed better results at low catalyst amounts. Furthermore, DMAP was readily removed from the products whereas metal catalysts can be hard to remove from the final material, potentially shortening the material lifespan and making it unfit for some applications. Therefore, the use of an easily removable and more efficient organocatalyst can be considered a good alternative to metal catalysts.
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•Organocatalytic asymmetric 3 + 3-cycloaddition is developed.•The method provides novel enantioenriched functionalized morpholin-3-one derivatives.•Chiral cinchonidine-derived ...squaramide is used as the organocatalyst.
An organocatalytic asymmetric 3 + 3-cycloaddition between γ-hydroxy-α,β-unsaturated ketones and in situ generated azaoxyallyl cations has been developed for the enantioselective synthesis of functionalized morpholin-3-ones. The asymmetric reaction using cinchonidine-derived squaramide as an organocatalyst was tolerant to various γ-hydroxy-α,β-unsaturated ketones and α-bromodimethylhydroxamates, providing access to the desired functionalized morpholin-3-ones in moderate yields with good-to-excellent enantioselectivities (up to 90% ee).
Cross‐Dehydrogenative Coupling The photocatalytic C1‐functionalization of 2‐aryltetrahydroisoquinolines by cross‐dehydrogenative coupling with nitroalkanes is a well‐established method for the ...preparation of 1‐nitroalkyl‐2‐aryl‐tetrahydroisoquinolines. In their Communication on page 8336 ff., M. Brasholz et al. describe that these primary coupling products readily undergo a subsequent oxidative cascade cyclization to furnish 12‐nitroindolo2,1‐aisoquinoline derivatives. Key to this hitherto unreported one‐pot transformation is the presence of a base, such as K3PO4 and aminoanthraquinones emerged as the ideal organic photocatalysts.
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•The first organo-catalyzed Michael addition of 2-fluoro-2-arylacetonitriles with activated alkenes.•A broad substrate scope with respect to the Michael acceptor.•The use of water as ...the reaction solvent.
An efficient synthesis of a variety of 2-arylacetonitriles containing a fluorinated stereogenic center through organo-catalyzed Michael addition reaction of 2-fluoro-2-arylacetonitriles has been developed. This protocol uses a cheap organocatalyst (DBU) and has a broad substrate scope: α, β-unsaturated ketones, esters, nitriles and sulfones were all successfully reacted. Importantly, water proved to be a good solvent for this reaction.
This review surveys the recent developments to perform heterogeneous catalysis in continuous‐flow microreactors. Three different types, namely, (i) packed‐bed, (ii) monolithic, and (iii) wall‐coated ...approaches are discussed to implement various kinds of catalysts in a microreactor. In addition, the applications of these supported catalysts to perform a variety of organic reactions are described. Furthermore, advantages of catalytic microreactors over classical batch reactors on one or more aspects of the reaction, such as rate, conversion, selectivity, and enantioselectivity are presented.
The direct catalytic C−H amination of arenes is a powerful synthetic strategy with useful applications in pharmaceuticals, agrochemicals, and materials chemistry. Despite the advances in catalytic ...C−H functionalization, the use of aliphatic amine coupling partners is limited. Described herein is the construction of C−N bonds, using primary amines, by direct C−H functionalization with an acridinium photoredox catalyst under an aerobic atmosphere. A wide variety of primary amines, including amino acids and more complex amines are competent coupling partners. Various electron‐rich aromatics and heteroaromatics are useful scaffolds in this reaction, as are complex, biologically active arenes. We also describe the ability to functionalize arenes that are not oxidized by an acridinium catalyst, such as benzene and toluene, thus supporting a reactive amine cation radical intermediate.
To be direct: The construction of C−N bonds from primary amines has been achieved by direct C−H functionalization with an acridinium photoredox catalyst under an aerobic conditions. The method tolerates a wide variety of primary amines, including amino acids, and the regiochemistry is influenced by the arene substitution pattern. Notably, the method can be used in a flow chemistry setup.
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