Pick your Pd partners: A number of catalytic systems have been developed for palladium-catalyzed CH activation/CC bond formation. Recent studies concerning the palladium(II)-catalyzed coupling of CH bonds with organometallic reagents through a PdII/Pd0 catalytic cycle are discussed (see scheme), and the versatility and practicality of this new mode of catalysis are presented. Unaddressed questions and the potential for development in the field are also addressed.

In the past decade, palladium-catalyzed CH activation/CC bond-forming reactions have emerged as promising new catalytic transformations; however, development in this field is still at an early stage compared to the state of the art in cross-coupling reactions using aryl and alkyl halides. This Review begins with a brief introduction of four extensively investigated modes of catalysis for forming CC bonds from CH bonds: PdII/Pd0, PdII/PdIV, Pd0/PdII/PdIV, and Pd0/PdII catalysis. A more detailed discussion is then directed towards the recent development of palladium(II)-catalyzed coupling of CH bonds with organometallic reagents through a PdII/Pd0 catalytic cycle. Despite the progress made to date, improving the versatility and practicality of this new reaction remains a tremendous challenge.

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Palladium(II)-catalyzed C-H activation/C-C cross-coupling reactions: versatility and practicality.

Complete Field Guide to Asymmetric BINOL-Phosphate Derived Brønsted Acid and Metal Catalysis: History and Classification by Mode of Activation; Brønsted Acidity, Hydrogen Bonding, Ion Pairing, and Metal Phosphates

The legacy of Gilbert Newton Lewis (1875-1946) pervades the lexicon of chemical bonding and reactivity. The power of his concept of donor-acceptor bonding is evident in the eponymous foundations of electron-pair acceptors (Lewis acids) and donors (Lewis bases). Lewis recognized that acids are not restricted to those substances that contain hydrogen (Bronsted acids), and helped overthrow the "modern cult of the proton". His discovery ushered in the use of Lewis acids as reagents and catalysts for organic reactions. However, in recent years, the recognition that Lewis bases can also serve in this capacity has grown enormously. Most importantly, it has become increasingly apparent that the behavior of Lewis bases as agents for promoting chemical reactions is not merely as an electronic complement of the cognate Lewis acids: in fact Lewis bases are capable of enhancing both the electrophilic and nucleophilic character of molecules to which they are bound. This diversity of behavior leads to a remarkable versatility for the catalysis of reactions by Lewis bases.

Lewis Base Catalysis in Organic Synthesis

Katalyse mit Methode: Eine ganze Reihe katalytischer Palladiumsysteme fur die C-H-Aktivierung/C-C-Kupplung (siehe Schema) wurde in jungerer Zeit entwickelt. Ein besonderer Schwerpunkt ist die PdII-katalysierte Kupplung von C-H-Bindungen mit metallorganischen Reagentien durch PdII/Pd0-Katalysezyklen. Die Vielseitigkeit dieser Katalysemethode wird demonstriert, zudem werden offene Fragen sowie das Entwicklungspotenzial des Gebietes angesprochen.

In den letzten zehn Jahren wurde die palladiumkatalysierte C-H-Aktivierung/C-C-Kupplung zu einer vielversprechenden katalytischen Umwandlung entwickelt. Allerdings sind die Moglichkeiten auf diesem Gebiet bisher noch nicht so umfangreich wie bei den Kreuzkupplungen, bei denen Aryl- und Alkylhalogenide eingesetzt werden. Dieser Aufsatz stellt vier ausfuhrlich untersuchte Katalysemethoden zur C-C-Bindungsbildung ausgehend von C-H-Bindungen vor: PdII/Pd0-, PdII/PdIV-, Pd0/PdII/PdIV- und Pd0/PdII-Katalyse. Auserdem werden neuere Entwicklungen bei der PdII-katalysierten Kupplung von C-H-Bindungen mit metallorganischen Reagentien durch einen PdII/Pd0-Katalysezyklus vorgestellt. Ungeachtet aller bisherigen Fortschritte verbleibt es eine wichtige Aufgabe, die Vielseitigkeit und Anwendbarkeit dieser Reaktionen auf eine breitere Grundlage zu stellen.

Palladium(II)‐katalysierte C‐H‐Aktivierung/C‐C‐Kreuzkupplung: Vielseitigkeit und Anwendbarkeit

Harnessing visible light to access excited (triplet) states of organic compounds can enable impressive reactivity modes. This tutorial review covers the photophysical fundamentals and most significant advances in the field of visible-light-mediated energy transfer catalysis within the last decade. Methods to determine excited triplet state energies and to characterize the underlying Dexter energy transfer are discussed. Synthetic applications of this field, divided into four main categories (cyclization reactions, double bond isomerizations, bond dissociations and sensitization of metal complexes), are also examined.

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Energy transfer catalysis mediated by visible light: principles, applications, directions

Mo and W MonoAryloxide-Pyrrolide (MAP) olefin metathesis catalysts can couple terminal olefins to give as high as >98% Z-products in moderate to high yields with as little as 0.2% catalyst. Results are reported for 1-hexene, 1-octene, allylbenzene, allyltrimethylsilane, methyl-10-undecenoate, methyl-9-decenoate, allylB(pinacolate), allylOBenzyl, allylNHTosyl, and allylNHPh. It is proposed that high Z-selectivity is achieved because a large aryloxide only allows metallacyclobutanes to form that contain adjacent cis substituents and because isomerization of Z-product to E-product can be slow in that same steric environment.

Highly Z-selective metathesis homocoupling of terminal olefins.

The first catalytic formal [5+4] cycloaddition to prepare nine-membered heterocycles is presented. Under palladium catalysis, the reaction of N-tosyl azadienes and substituted vinylethylene carbonates (VECs) proceeds smoothly to produce benzofuran-fused heterocycles in uniformly high efficiency. Highly diastereoselective functionalization of the nine-membered heterocycles through peripheral attack is also demonstrated.

Construction of Nine-Membered Heterocycles through Palladium-Catalyzed Formal [5+4] Cycloaddition

Here, we present an unprecedented formal [3 + 2] cycloaddition of para-quinone methides with vinyl epoxides/cyclopropanes to deliver a wide range of spiro[4.5]decanes in high efficiency and stereoselectivity. The commercial availability of the catalysts and reagents, together with the convenient procedure, makes it an attractive method in asymmetric synthesis.

Stereoselective 1,6-Conjugate Addition/Annulation of para-Quinone Methides with Vinyl Epoxides/Cyclopropanes

The first enantioselective formal [5+4] cycloaddition is realized under palladium catalysis to deliver benzofuran-fused nine-membered rings. These medium-sized heterocycles and derivatives undergo unique rearrangements induced by transannular bond formation, resulting in the production of two classes of densely substituted polycyclic heterocycles in excellent efficiency and stereoselectivity.

Nine-Membered Benzofuran-Fused Heterocycles: Enantioselective Synthesis by Pd-Catalysis and Rearrangement via Transannular Bond Formation

The catalytic asymmetric reduction of ketimines has been explored extensively for the synthesis of chiral amines, with reductants ranging from Hantzsch esters, silanes, and formic acid to H2 gas. Alternatively, the amination of alcohols by the use of borrowing hydrogen methodology has proven a highly atom economical and green method for the production of amines without an external reductant, as the alcohol substrate serves as the H2 donor. A catalytic enantioselective variant of this process for the synthesis of chiral amines, however, was not known. We have examined various transition-metal complexes supported by chiral ligands known for asymmetric hydrogenation reactions, in combination with chiral Bronsted acids, which proved essential for the formation of the imine intermediate and the transfer-hydrogenation step. Our studies led to an asymmetric amination of alcohols to provide access to a wide range of chiral amines with good to excellent enantioselectivity.

Catalytic enantioselective amination of alcohols by the use of borrowing hydrogen methodology: cooperative catalysis by iridium and a chiral phosphoric acid.

Yu Zhao

Papers

Highly Z-selective metathesis homocoupling of terminal olefins.

Construction of Nine-Membered Heterocycles through Palladium-Catalyzed Formal [5+4] Cycloaddition

Stereoselective 1,6-Conjugate Addition/Annulation of para-Quinone Methides with Vinyl Epoxides/Cyclopropanes

Nine-Membered Benzofuran-Fused Heterocycles: Enantioselective Synthesis by Pd-Catalysis and Rearrangement via Transannular Bond Formation

Catalytic enantioselective amination of alcohols by the use of borrowing hydrogen methodology: cooperative catalysis by iridium and a chiral phosphoric acid.