C–H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C–H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C–H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C–H activation until summer 2018.

3d Transition Metals for C-H Activation.

The development of new methods for the direct functionalization of unactivated C–H bonds is ushering in a paradigm shift in the field of retrosynthetic analysis. In particular, the catalytic enantioselective functionalization of C–H bonds represents a highly atom- and step-economic approach toward the generation of structural complexity. However, as a result of their ubiquity and low reactivity, controlling both the chemo- and stereoselectivity of such processes constitutes a significant challenge. Herein we comprehensively review all asymmetric transition-metal-catalyzed methodologies that are believed to proceed via an inner-sphere-type mechanism, with an emphasis on the nature of stereochemistry generation. Our analysis serves to document the considerable and rapid progress within in the field, while also highlighting limitations of current methods.

/pdf/catalytic-enantioselective-transformations-involving-c-h-4dm3wav9qj.pdf

Catalytic Enantioselective Transformations Involving C-H Bond Cleavage by Transition-Metal Complexes.

Four-coordinate organoboron compounds with rigid π-conjugated structures are intensely luminescent and have high carrier mobility which enables them to be applied in optoelectronics including organic light-emitting diodes (OLEDs), organic field-effect transistors, as well as photoresponsive, sensory and imaging materials. Various chelate ligands and boron moieties have been explored to construct proper electronic structures and suitable molecular arrangements, which play important roles on the photophysical and electronic properties of the four coordinate boron compounds. These efforts have produced a number of fascinating molecules, some of which have exhibited high performance as light emitting materials. In this article, we provide an overview of the progress in the molecular construction of four-coordinate organoboron compounds with an emphasis on their applications in OLEDs.

Four-coordinate organoboron compounds for organic light-emitting diodes (OLEDs).

γ-Butenolides, γ-butyrolactones, and derivatives, especially in enantiomerically pure form, constitute the structural core of numerous natural products which display an impressive range of biological activities which are important for the development of novel physiological and therapeutic agents. Furthermore, optically active γ-butenolides and γ-butyrolactones serve also as a prominent class of chiral building blocks for the synthesis of diverse biological active compounds and complex molecules. Taking into account the varying biological activity profiles and wide-ranging structural diversity of the optically active γ-butenolide or γ-butyrolactone structure, the development of asymmetric synthetic strategies for assembling such challenging scaffolds has attracted major attention from synthetic chemists in the past decade. This review offers an overview of the different enantioselective synthesis of γ-butenolides and γ-butyrolactones which employ catalytic amounts of metal complexes or organocatalysts, wit...

/pdf/catalytic-asymmetric-synthesis-of-butenolides-and-2ircj0zqvr.pdf

Catalytic Asymmetric Synthesis of Butenolides and Butyrolactones

ConspectusThe implementation of any chemical reaction in a structurally complex setting (King, S. M. J. Org. Chem. 2014, 79, 8937) confronts structurally defined barriers: steric environment, functional group reactivity, product instability, and through-bond electronics. However, there are also practical barriers. Late-stage reactions conducted on small quantities of material are run inevitably at lower than optimal concentrations. Access to late-stage material limits extensive optimization. Impurities from past reactions can interfere, especially with catalytic reactions. Therefore, chemical reactions on which one can rely at the front lines of a complex synthesis campaign emerge from the crucible of total synthesis as robust, dependable, and widely applied. Trost conceptualized “chemoselectivity” as a reagent’s selective reaction of one functional group or reactive site in preference to others (Trost, B. M. Science 1983, 219, 245). Chemoselectivity and functional group tolerance can be evaluated quickly...

The High Chemofidelity of Metal-Catalyzed Hydrogen Atom Transfer.

A four-coordinate organoboron compound B(ppy)Mes2 (1, ppy=2-phenylpyridyl, Mes=mesityl) was previously found to undergo reversible photochromic switching through the formation/breaking of a CC bond, accompanied by a dramatic color change from colorless to dark blue. To understand this unusual phenomenon, a series of new four-coordinate boron compounds based on the ppy-chelate ligand and its derivatives have been synthesized. In addition, new N,C-chelate ligands based on benzo[b]thiophenylpyridine and indolylpyridine have also been synthesized and their boron compounds were investigated. The crystal structures of most of the new compounds were determined by X-ray diffraction analysis. UV/Vis, NMR, and electrochemical methods were used to monitor the photoisomerization process. DFT calculations were performed for all compounds to understand the photophysical and electronic properties of this class of molecules. The results of our study showed that the bulky mesityl group is necessary for photochromic switching. Electron-donating and electron-withdrawing groups on the ppy chelate have a distinct impact on the photoisomerization rate and the photochemical stability of the molecule. Furthermore, we have found that the non-ppy-based N,C-chelate ligands such as benzo[b]thiophenepyridyl can also promote photoisomerization of the boron chromophore in the same manner as the ppy chelate, but the product is thermally unstable.

Steric and Electronic Influence on Photochromic Switching of N,C‐Chelate Four‐Coordinate Organoboron Compounds

An enantioselective ketone hydroacylation enables the direct preparation of lactones from keto alcohols. The alcohol is oxidized in situ to an aldehyde, obviating the need to prepare sensitive keto aldehyde substrates. Noyori’s asymmetric transfer hydrogenation catalyst was applied to address challenges of reactivity, chemoselectivity, and enantioselectivity.

Enantioselective Ketone Hydroacylation Using Noyori’s Transfer Hydrogenation Catalyst

We report an intermolecular hydroacylation of allylic alcohols with salicylaldehydes to afford β-hydroxy aryl ketones in 73–94% yields as single regioisomers. The reactivity and regioselectivity were promoted by catalytic amounts of a phosphinite that forms a dynamic covalent bond with the allylic alcohol. Hydroacylation of 1,2- and 1,1-disubstituted olefins generates β-hydroxy aryl ketones bearing tertiary and quaternary centers, respectively.

β-hydroxy ketones prepared by regioselective hydroacylation

Catalytic Hydroacylation as an Approach to Homoaldol Products

Switching of a Single Boryl Center in π‐Conjugated Photochromic Polyboryl Compounds and Its Impact on Fluorescence Quenching

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