Copper-Catalyzed Oxidative Coupling of Alkenes with Aldehydes: Direct Access to α,β-Unsaturated Ketones

Functionality-Directed Regio- and Enantio-Selective Olefinic C-H Functionalization of Aryl Alkenes

Aryl alkenes represents one of the most widely occurring structural motif in countless drugs and natural products, and direct C-H functionalization of aryl alkenes provides atom- step efficient access toward valuable analogues. Among them, group-directed selective olefinic α- and β-C-H functionalization, bearing a directing group on the aromatic ring, has attracted remarkable attentions, including alkynylation, alkenylation, amino-carbonylation, cyanation, domino cyclization and so on. These transformations proceed by endo- and exo-C-H cyclometallation and provide aryl alkene derivatives in excellent site- stereo-selectivity. Enantio-selective α- and β- olefinic C-H functionalization were also covered to synthesis axially chiral styrenes.

Direct Aroylation of Olefins through a Cobalt/Photoredox-Catalyzed Decarboxylative and Dehydrogenative Coupling with α-Oxo Acids

A photoredox/cobalt dual catalytic procedure has been developed that allows benzoylation of olefins. Here the photoredox catalyst effects the decarboxylation of α-ketoacids to form benzoyl radicals. After addition of this radical to styrenes, the cobalt catalyst abstracts a H-atom. Hydrogen evolution from the putative cobalt hydride intermediate allows a Heck-like aroylation without the need for a stoichiometric oxidant. Mechanistic studies reveal that electronically different styrenes lead to a curved Hammett plot, thus suggesting a change in product-determining step in the catalytic mechanism.

Synthesis of Ketones by C-H Functionalization of Aldehydes with Boronic Acids under Transition-Metal-Free Conditions

A method for the synthesis of ketones from aldehydes and boronic acids via a transition-metal-free C-H functionalization reaction is reported. The method employs nitrosobenzene as a reagent to drive the simultaneous activation of the boronic acid as a boronate and the activation of the C-H bond of the aldehyde as an iminium species that triggers the key C-C bond-forming step via an intramolecular migration from boron to carbon. These findings constitute a practical, scalable, and operationally straightforward method for the synthesis of ketones.

Copper-Catalyzed 1,2-Methoxy Methoxycarbonylation of Alkenes with Methyl Formate

Reported here is a copper-catalyzed 1,2-methoxy methoxycarbonylation of alkenes by an unprecedented use of methyl formate as a source of both the methoxy and the methoxycarbonyl groups. This reaction transforms styrene and its derivatives into value-added β-methoxy alkanoates and cinnamates, as well as medicinally important five-membered heterocycles, such as functionalized tetrahydrofurans, γ-lactones, and pyrrolidines. A ternary β-diketiminato-Cu^I -styrene complex, fully characterized by NMR spectroscopy and X-ray crystallographic analysis, is capable of catalyzing the same transformation. These findings suggest that pre-coordination of electron-rich alkenes to copper might play an important role in accelerating the addition of nucleophilic radicals to electron-rich alkenes, and could have general implications in the design of novel radical-based transformations.

β-Selective Aroylation of Activated Alkenes by Photoredox Catalysis

Late-stage synthesis of α,β-unsaturated aryl ketones remains an unmet challenge in organic synthesis. Reported herein is a photocatalytic non-chain-radical aroyl chlorination of alkenes by a 1,3-chlorine atom shift to form β-chloroketones as masked enones that liberate the desired enones upon workup. This strategy suppresses side reactions of the enone products. The reaction tolerates a wide array of functional groups and complex molecules including derivatives of peptides, sugars, natural products, nucleosides, and marketed drugs. Notably, addition of 2,6-di-tert-butyl-4-methyl-pyridine enhances the quantum yield and efficiency of the cross-coupling reaction. Experimental and computational studies suggest a mechanism involving PCET, formation and reaction of an α-chloro-α-hydroxy benzyl radical, and 1,3-chlorine atom shift.

Mechanistic view of Ru-catalyzed C-H bond activation and functionalization: computational advances

Ru-Catalyzed aromatic C-H bond activation and functionalization have emerged as important topics because they have resulted in remarkable progress in organic synthesis. Both experimental and theoretical studies of their mechanisms are important for the design of new synthetic methodologies. In this review, a mechanistic view of the Ru-mediated C-H bond cleavage step is first given to reveal the C-H bond activation modes, including oxidative addition, metathesis and base-assisted deprotonation. In this process, directing groups play an important role in determining the reactivity of the C-H bond. The C-H bond activation generally leads to the formation of a Ru-C bond, which is further functionalized in the subsequent steps. The mechanisms of Ru-catalyzed arylation, alkylation, and alkenylation of arenes are summarized, and these transformations can be categorized into cross-coupling with electrophiles or oxidative coupling with nucleophiles. In addition, the mechanism of ortho-ruthenation-enabled remote C-H bond functionalization is also discussed.

Cu-Catalyzed Cross-Dehydrogenative ortho-Aminomethylation of Phenols

A highly selective Cu^II‐catalyzed cross‐dehydrogenative ortho‐aminomethylation of phenols with aniline derivatives is described. The corresponding C(sp²)−C(sp³) coupling products were obtained in moderate to excellent yields under mild reaction conditions and with a broad substrate scope. A radical mechanism is proposed.

Design and synthesis of bi-functional Co-containing zeolite ETS-10 catalyst with high activity in the oxidative coupling of alkenes with aldehydes for preparing α,β-epoxy ketones

Developing highly efficient heterogeneous catalysts for organic synthesis is of great importance in modern synthetic chemistry.

Photocatalytic Dehydrogenative Cross-Coupling of Alkenes with Alcohols or Azoles without External Oxidant

Direct cross-coupling between alkenes/R-H or alkenes/RXH is a dream reaction, especially without external oxidants. Inputting energy by photocatalysis and employing a cobalt catalyst as a two-electron acceptor, a direct C-H/X-H cross-coupling with H₂ evolution has been achieved for C-O and C-N bond formation. A new radical alkenylation using alkene as the redox compound is presented. A wide range of aliphatic alcohols-even long chain alcohols-are tolerated well in this system, providing a new route to multi-substituted enol ether derivatives using simple alkenes. Additionally, this protocol can also be used for N-vinylazole synthesis. Mechanistic insights reveal that the cobalt catalyst oxidizes the photocatalyst to revive the photocatalytic cycle.

A transition-metal-free, one-pot procedure for the synthesis of α,β-epoxy ketones by oxidative coupling of alkenes and aldehydes via base catalysis

A new strategy for the synthesis of epoxides is presented. This process allows the direct synthesis of epoxides from alkenes and aldehydes through C-H functionalization and C-C/C-O bond formation.