Gillesds

The direct functionalization of C−H bonds is among the most important transformations in organic synthesis, but its efficiency depends on its selectivity that can be controlled by the innate reactivity of the substrate or a directing group. We review and discuss in a comprehensive manner C−H functionalization processes based on the transient directing group strategy. For more information, see the Review by Gwilherm Evano et al. on page 13899.

A hierarchically porous defective UiO-66 (d-UiO-66) integrated with MoS₂ nanosheets is fabricated in the Communication on page 24849 by Xu Jing, Chunying Duan et al. The composite is effective for the photocatalytic conversion of gas-phase CO₂ and H₂O into CH₃COOH and O₂ under visible light irradiation. The Mo-O-Zr bimetallic sites on the interface between UiO-66 and MoS₂ play a key role in achieving high selectivity for C2 production.

The frustrated Lewis pair (FLP), 2,6-lutidine/ B(C₆F₅)₃ mediates the catalytic reduction of CO₂ using H₂ and a silylhalide. Control of the silylhalide and solvent, affords selective avenues to the disilylacetal (R₃SiOCH₂OSiR₃), methoxysilane (R₃SiOCH₃), methyliodide (CH₃I) and methane (CH₄) under mild conditions. The mechanism is studied by DFT and accounts for the observed selectivity.

Abstract

The frustrated Lewis pair (FLP) derived from 2,6-lutidine and B(C₆F₅)₃ is shown to mediate the catalytic hydrogenation of CO₂ using H₂ as the reductant and a silylhalide as an oxophile. The nature of the products can be controlled with the judicious selection of the silylhalide and the solvent. In this fashion, this metal-free catalysis affords avenues to the selective formation of the disilylacetal (R₃SiOCH₂OSiR₃), methoxysilane (R₃SiOCH₃), methyliodide (CH₃I) and methane (CH₄) under mild conditions. DFT studies illuminate the complexities of the mechanism and account for the observed selectivity.

Upgrading biomass without waste: Scientists from Rostock and Lanzhou have, for the first time, succeeded in directly converting C₂−C₃ biomass molecules with amines and H₂O₂ to industrially important formamides by valorizing all carbon atoms of the substrates without producing undesired by-products. The reaction is catalyzed under very mild conditions by a 5A zeolite with active Cu^II single sites; ^.NHPh and ^.OOH radicals play a key role. More information can be found in the Full Paper by A. Brückner, F. Shi et al. (DOI: 10.1002/chem.202102300).

The Cover Feature shows the vacancy engineering of transition metal sulfide and oxide catalysts, which effectively affect the hydrodeoxygenation of lignin-derived oxygenates into high-value chemicals, therefore providing new ideas for solving energy problems. More information can be found in the Minireview by S. Jiang et al.

Synlett
DOI: 10.1055/s-0040-1720920

Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Synlett
DOI: 10.1055/a-1608-5069

Phenols are important components of pharmaceuticals, biologically active natural products, and materials. Here, we briefly discuss recent advances in catalytic hydroxylation reactions for the synthesis of phenols, with particular attention to our recent work. H2O is proved to be an efficient hydroxide reagent in converting (hetero)aryl halides into the corresponding phenols under synergistic organophotoredox and nickel catalysis. Aryl bromides as well as less reactive aryl chlorides show high reactivity in this catalytic system. This methodology can be applied to the efficient synthesis of diverse phenols and allows the hydroxylation of multifunctional pharmaceutically relevant aryl halides.1 Introduction2 Representative Methods for Transition-Metal-Catalyzed Hydroxylation of (Hetero)Aryl Halides3 Organophotoredox/Ni Dual Catalytic Hydroxylation of Aryl Halides with Water4 Summary and Outlook
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Publication date: Available online 29 September 2021

Source: Chem

Author(s): Sebastian B. Beil

Among the different reactions that lead to the formation of C−C bonds, the Suzuki-Miyaura approach has a fundamental role, at the level of basic research and industrial applications. In particular, the palladium is usually the metal of the corresponding catalyst. The complexity of the reaction lies in the individual steps of the cycle, as well as in the generation of the catalytically active species. Here, through a chronology from the beginnings of cross coupling, how far the field has come is analyzed. For more information, see the Review by S. P. Nolan, A. Poater et al. on page 13481.

Mesoporous catalysts: This review presents an overview of the recent advances in the development of titanosilicate catalysts used in epoxidation and critically addresses the key relation between the preparation method and the physico-chemical properties that govern catalytic performance.

Abstract

Epoxidation reactions are tremendously important for modern chemistry, as they lead to series of highly useful bulk and fine chemicals, monomers, and intermediates for organic synthesis. Progress in epoxidation processes goes hand in hand with the advancement made in catalysis science. In this context, heterogeneous catalysts, and particularly Ti-based formulations, are playing a central role and have seen tremendous developments over the past two decades, leveraging on advanced materials science. The aim of this review is to illustrate the various strategies of titanosilicate catalysts preparation that can lead to more versatile, more performant, and greener epoxidation processes. We successively cover (i) supported catalysts, obtained by the grafting of Ti species onto preformed silica supports, (ii) microporous crystalline titanosilicates (zeolites), and (iii) amorphous titanosilicates obtained by sol-gel chemistry. For each category, with an emphasis on catalyst preparation, the challenges that have to be tackled to boost catalyst performance are highlighted. From that point, we present a critical review of the different approaches that have been proposed in the primary literature to tailor the properties that govern catalysts performance (activity, selectivity, stability, ease of handling). This is done by better controlling the nature of the active surface species, adapting particles size and shape, optimizing texture, modifying surface chemistry, etc. These lines of attack encompass molecular approaches for the grafting of well-defined species, top-down and bottom-up synthesis of hierarchically porous zeolites, advanced sol-gel routes potentially performed in non-conventional media or coupled with original processing, preparation of self-standing monoliths, etc. Future research directions are discussed with emphasis on the application scope of new catalytic materials and possible approaches to increase catalyst performance.

Synlett
DOI: 10.1055/s-0040-1720889

Under thermal conditions, 1,4,2-dioxazol-5-ones are known to undergo decarboxylation followed by Lossen’s rearrangement to yield isocyanates. Described herein is the in situ trapping of the resulting isocyanates with carbon nucleophiles to synthesize β-keto amides. Furthermore, a general and mild method for the conversion of the resulting β-keto amides into quinolin-2-ones is reported.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Synlett
DOI: 10.1055/a-1637-9308

Metal hydride catalyzed remote hydrofunctionalization has attracted extensive attention in the past decade, as it provides a complementary approach for selective functionalization of remote C(sp3)–H bonds. Recently, a wide variety of olefinic remote hydrofunctionalization reactions have been realized through the synergistic combination of NiH-catalyzed chain-walking and Ni-catalyzed cross-coupling. In this Account we discuss our recent achievements in the remote hydroarylation of olefins and in asymmetric hydroarylation.1 Introduction2 NiH-Catalyzed Remote Hydroarylation3 Progress in Asymmetric Catalysis4 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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