Photo‐Induced Ruthenium‐Catalyzed C−H Arylations at Ambient Temperature

Ambient temperature ruthenium‐catalyzed C?H arylations were accomplished by visible light without additional photocatalysts. The robustness of the ruthenium‐catalyzed C?H functionalization protocol was reflected by a broad range of sensitive functional groups and synthetically useful pyrazoles, triazoles and sensitive nucleosides and nucleotides, as well as multifold C?H functionalizations. Biscyclometalated ruthenium complexes were identified as the key intermediates in the photoredox ruthenium catalysis by detailed computational and experimental mechanistic analysis. Calculations suggested that the in situ formed photoactive ruthenium species preferably underwent an inner‐sphere electron transfer.     

Pd(0)‐Catalyzed Direct C−H Functionalization of 2‐H‐4‐Benzylidene Imidazolones: Friendly and Large‐Scale Access to GFP and Kaede Protein Fluorophores

The first one‐pot synthesis of N‐substituted 2‐H‐4‐benzylidene imidazolones and their subsequent palladium‐catalyzed and copper‐assisted direct C2?H arylation and alkenylation with aryl‐ and alkenylhalides are described. This innovative synthesis is step‐economical, azide‐free, high yielding, highly flexible in the introduction of a variety of electronically different groups, and can be operated on large‐scale. Moreover, the method allows direct access to C2‐arylated or alkenylated imidazolone‐based green fluorescent protein (GFP) and Kaede protein fluorophores, including ortho‐hydroxylated models.     

Whole‐Cell Biocatalysts for Stereoselective C−H Amination Reactions

Enantiomerically pure chiral amines are ubiquitous chemical building blocks in bioactive pharmaceutical products and their synthesis from simple starting materials is of great interest. One of the most attractive strategies is the stereoselective installation of a chiral amine through C?H amination, which is a challenging chemical transformation. Herein we report the application of a multienzyme cascade, generated in a single bacterial whole‐cell system, which is able to catalyze stereoselective benzylic aminations with ee values of 97.5 %. The cascade uses four heterologously expressed recombinant enzymes with cofactors provided by the host cell and isopropyl amine added as the amine donor. The cascade presents the first example of the successful de novo design of a single whole‐cell biocatalyst for formal stereoselective C?H amination.     

Nickela‐electrocatalyzed Mild C−H Alkylations at Room Temperature

Direct alkylations of carboxylic acid derivatives are challenging and particularly nickel catalysis commonly requires high reaction temperatures and strong bases, translating into limited substrate scope. Herein, nickel‐catalyzed C?H alkylations of unactivated 8‐aminoquinoline amides have been realized under exceedingly mild conditions, namely at room temperature, with a mild base and a user‐friendly electrochemical setup. This electrocatalyzed C?H alkylation displays high functional group tolerance and is applicable to both the primary and secondary alkylation. Based on detailed mechanistic studies, a nickel(II/III/I) catalytic manifold has been proposed.     

Photoinduced Copper‐Catalyzed C−H Arylation at Room Temperature

Room‐temperature azole C?H arylations were accomplished with inexpensive copper(I) compounds by means of photoinduced catalysis. The expedient copper catalysis set the stage for site‐selective C?H arylations of non‐aromatic oxazolines under mild reaction conditions, and provides step‐economical access to the alkaloid natural products balsoxin and texamine.     

Nickel‐Catalyzed Arylation,Alkenylation, and Alkynylation of Unprotected Thioglycosides at Room Temperature

Unprotected thioglycosides were effective nucleophiles for Ni⁰‐catalyzed C? S bond‐forming reaction with functionalized (hetero)aryl, alkenyl, and alkynyl halides. The functional‐group tolerance on the electrophilic partner was typically high and the anomeric selectivities of the thioglycosides were high in all cases. The efficiency of this general procedure was well‐demonstrated by the synthesis of 4‐methyl‐7‐thioumbelliferyl‐β‐D ‐cellobioside (MUS‐CB).     

Sterically Congested 2,6‐Disubstituted Anilines from Direct C−N Bond Formation at an Iodine(III) Center

2,6‐Disubstituted anilines are readily prepared from the direct reaction between amides and diaryliodonium salts. As demonstrated for 24 different examples, the reaction is of unusually broad scope with respect to the sterically congested arene and the nitrogen source, occurs without the requirement for any additional promoter, and proceeds through a direct reductive elimination at the iodine(III) center. The efficiency of the coupling procedure is further demonstrated within the short synthesis of a chemerin binding inhibitor.     

Visible‐Light‐Enabled Ruthenium‐Catalyzed meta‐C−H Alkylation at Room Temperature

Visible‐light‐induced ruthenium catalysis has enabled remote C?H alkylations with excellent levels of position control under exceedingly mild conditions at room temperature. The metallaphotocatalysis occurred under exogenous‐photosensitizer‐free conditions and features an ample substrate scope. The robust nature of the photo‐induced mild meta‐C?H functionalization is reflected by the broad functional group tolerance, and the reaction can be carried out in an operationally simple manner, setting the stage for challenging secondary and tertiary meta‐C?H alkylations by ruthenaphotoredox catalysis.     

Reversible Photoswitching of RNA Hybridization at Room Temperature with an Azobenzene C‐Nucleoside

Photoregulation of RNA remains a challenging task as the introduction of a photoswitch entails changes in the shape and the stability of the duplex that strongly depend on the chosen linker strategy. Herein, the influence of a novel nucleosidic linker moiety on the photoregulation efficiency of azobenzene is investigated. To this purpose, two azobenzene C‐nucleosides were stereoselectively synthesized, characterized, and incorporated into RNA oligonucleotides. Spectroscopic characterization revealed a reversible and fast switching process, even at 20 °C, and a high thermal stability of the respective cis isomers. The photoregulation efficiency of RNA duplexes upon trans‐to‐cis isomerization was investigated by using melting point studies and compared with the known D ‐threoninol‐based azobenzene system, revealing a photoswitching amplitude of the new residues exceeding 90 % even at room temperature. Structural changes in the duplexes upon photoisomerization were investigated by using MM/MD calculations. The excellent photoswitching performance at room temperature and the high thermal stability make these new azobenzene residues promising candidates for in‐vivo and nanoarchitecture photoregulation applications of RNA.     

Development of a Simple Adjustable Zinc Acid/Base Hybrid Catalyst for C−C and C−O Bond‐Forming and C−C Bond‐Cleavage Reactions

A newly designed zinc Lewis acid/base hybrid catalyst was developed. By adjusting the Lewis acidity of the zinc center, aldol‐type additions of 2‐picolylamine Schiff base to aldehydes proceeded smoothly to afford syn‐aldol adduct equivalents, trans‐N,O‐acetal adducts, in high yields with high selectivities. NMR experiments, including microchanneled cell for synthesis monitoring (MICCS) NMR analysis, revealed that anti‐aldol adducts were formed at the initial stage of the reactions under kinetic control, but the final products were the trans‐(syn)‐N,O‐acetal adducts that were produced through a retro‐aldol process under thermodynamic control. In the whole reaction process, the zinc catalyst played three important roles: i) promotion of the aldol process (C?C bond formation), ii) cyclization process to the N,O‐acetal product (C?O bond formation), and iii) retro‐aldol process from the anti‐aldol adduct to the syn‐aldol adduct (C?C bond cleavage and C?C bond formation).     

Iron‐Catalyzed Oxidative Heterocoupling Between Aliphatic and Aromatic Organozinc Reagents: A Novel Pathway for Functionalized Aryl–Alkyl Cross‐Coupling Reactions

Aryl–alkyl cross‐coupling products are obtained by the iron‐catalyzed oxidative heterocoupling of organozinc reagents under mild conditions. This novel reaction pathway is versatile, allowing for the use of primary and secondary aliphatic diorganozinc reagents as coupling partners as well as tolerating functionalized aryl‐ and alkylzinc reagents.

     

氯化钯多相催化无配体室温Suzuki-Miyaura反应

本文报道了温和及有效的氯化钯多相催化无配体Suzuki-Miyaura反应,反应在室温、敞口容器和短时间内完成。各种碘代芳烃、溴代芳烃和活泼的氯代芳烃与四苯硼钠和芳香有机硼酸偶联高产率生成相应的产物,而且催化剂可循环使用4次不降低活性。     

Cobalt‐Catalyzed sp2‐C−H Activation: Intermolecular Heterocyclization with Allenes at Room Temperature

The reactivity of allenes in transition‐metal‐catalyzed C?H activation chemistry is governed by the formation of either alkenyl–metal (M–alkenyl) or metal–π‐allyl intermediates. Although either protonation or a β‐hydride elimination is feasible with a M–alkenyl intermediate, cyclization has remained unexplored to date. Furthermore, due to the increased steric hindrance, the regioselectivity for the intramolecular cyclization of the metal–π‐allyl intermediate was hampered towards the more substituted side. To address these issues, a unified approach to synthesize a diverse array of biologically and pharmaceutically relevant heterocyclic moieties by cobalt‐catalyzed directed C?H functionalization was envisioned. Upon successful implementation, the present strategy led to the regioselective formation of dihydroisoquinolin‐1(2H)‐ones, isoquinolin‐1(2H)‐ones, dihydropyridones, and pyridones.     

Surfactant‐Assisted Nanocrystalline Zinc Coordination Polymers: Controlled Particle Sizes and Synergistic Effects in Catalysis

Different morphologies and particle sizes of two crystalline zinc‐based coordination polymers (CPs), [Zn(pytz)H₂O]_n ( 1 ; H₂pytz=2,6‐bis(tetrazole)pyridine) and [Zn₂(pytz)₂4 H₂O] ( 2 ), from the bulk scale to the nanoscale, could be obtained under solvothermal conditions with different surfactants (polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) 2000) as templates. PVP and PEG 2000 could act as capping and structure‐directing agents, respectively, to influence the growth of crystalline particles and control their sizes. CP 1 exhibits a two‐dimensional framework with window‐like units and 2 shows a bimetallic structure. Nanocrystalline 1 and 2 were used as heterogeneous catalysts to study how adjacent catalytic active sites synergistically effected their catalytic reactivities in the direct catalytic conversion of aromatic dinitriles into oxazolines. The results showed that 1 produced bis‐oxazolines as the sole products, whereas 2 gave the mono‐oxazolines as the major products under the same reaction conditions.     

Micellar Catalysis for Ruthenium(II)‐Catalyzed C−H Arylation: Weak‐Coordination‐Enabled C−H Activation in H2O

Chemoselective C?H arylations were accomplished through micellar catalysis by a versatile single‐component ruthenium catalyst. The strategy provided expedient access to C?H‐arylated ferrocenes with wide functional‐group tolerance and ample scope through weak chelation assistance. The sustainability of the C?H arylation was demonstrated by outstanding atom‐economy and recycling studies. Detailed computational studies provided support for a facile C?H activation through thioketone assistance.     

Palladium(II)‐N‐Heterocyclic Carbene Complexes: Efficient Catalysts for the Direct C‐H Bond Arylation of Furans with Aryl Halides

This paper contains the synthesis and characterization of the seven new benzimidazolium salts and their corresponding new palladium(II)‐NHC complexes with the general formula [PdX₂(NHC)₂], (NHC = N‐heterocyclic carbene, X = Cl or Br), and also their catalytic activity in direct C‐H bond arylation of 2‐substituted furan derivatives with aryl bromides and aryl chlorides. Under the optimal conditions, these palladium(II)‐NHC complexes showed the good catalytic performance for the direct C‐H bond arylation of 2‐substituted furans with (hetero)aryl bromides, and with readily available and inexpensive aryl chlorides. The C‐H bond arylation regioselectively produced C5‐arylated furans by using 1 mol% of the palladium(II)‐NHC catalysts in moderate to high yields.     

Electrochemical C−H/N−H Activation by Water‐Tolerant Cobalt Catalysis at Room Temperature

Electrochemistry enabled C?H/N?H functionalizations at room temperature by external oxidant‐free cobalt catalysis. Thus, the sustainable cobalt electrocatalysis manifold proceeds with excellent levels of chemoselectivity and positional selectivity, and with ample scope, thus allowing electrochemical C?H activation under exceedingly mild reaction conditions at room temperature in water.     

A Facile Process for the Preparation of Three‐Dimensional Hollow Zn(OH)2 Nanoflowers at Room Temperature

A facile strategy has been developed to synthesize double‐shelled Zn(OH)₂ nanoflowers (DNFs) at room temperature. The nanoflowers were generated via conversion of Cu₂O nanoparticles (NPs) using ZnCl₂ and Na₂S₂O₃ by a simple process. Outward diffusion of the Cu²⁺, produced by an oxidation process on the surface of NPs, and the inward diffusion of Zn²⁺ by coordination and migration, eventually lead to a hollow cavity in the inner NPs with a double‐shelled 3D hollow flower shapes. The thickness of the inner and outer shells is estimated to be about 20 nm, and the thickness of nanopetals is about 7 nm. The nanoflowers have large surface areas and excellent adsorption properties. As a proof of potential applications, the DNFs exhibited an excellent ability to remove organic molecules from aqueous solutions.