Cobalt-Catalyzed Deprotection of Allyl Carboxylic Esters Induced by Hydrogen Atom Transfer

Advancing Propylene Epoxidation: the Role of Ethyl Acetate Autoxidation via Cobalt-Nickel Catalyzed C(acyl)─O Bond Scission

The selective autoxidation for the synthesis of valuable oxygenates has provoked keen interest from both academic and industrial sectors. Although the generation of reactive oxygen species via oxygen attack on C─H bonds near ester linkages is well-established, research into aliphatic ester oxidation has primarily focused on combustion, neglecting their potential utility in oxidation processes. Herein, a protocol for producing propylene oxide through the autoxidation of ethyl acetate in tandem with propylene epoxidation is demonstrated. The ethoxy radical, generated by ester C(acyl)─O bond cleavage in situ, subsequently underwent proton-coupled electron transfer with the Co(OAc)(μ-H2O)2Ni, followed by the formation of the peracetic acid optimally suited for the epoxidation reaction. The research not only eliminates the need for co-substrates in the epoxidation process but also fills the application gap in bulk-ester autoxidation, offering insights into the effective utilization of oxy-intermediates in autoxidation reactions.

Catalytic Asymmetric 1,4-Hydrocarbonation of 1,3-Enynes via Photoredox/Cobalt/Chromium Triple Catalysis

A synergistic photoredox/cobalt/chromium triple catalysis system for regioselective, enantioselective, and diastereoselective 1,4-hydrocarbonation of readily available 1,3-enyne precursors was explored, providing a modular synthetic platform for various trisubstituted axially chiral allenes bearing an extra central chirality. The protocol features a broad substrate scope, good functional group tolerance, excellent selectivity, and mild reaction conditions. Furthermore, a possible reaction mechanism is proposed based on numerous control experiments and density functional theory calculations.

Development of a nitrogen-bound hydrophobic auxiliary: application to solid/hydrophobic-tag relay synthesis of calpinactam

In the last couple of decades, technologies and strategies for peptide synthesis have advanced rapidly. Although solid-phase peptide synthesis (SPPS) and liquid-phase peptide synthesis (LPPS) have contributed significantly to the development of the field, there have been remaining challenges for C-terminal modifications of peptide compounds in SPPS and LPPS. Orthogonal to the current standard approach that relies on installation of a carrier molecule at the C-terminus of amino acids, we developed a new hydrophobic-tag carbonate reagent which facilitated robust preparation of nitrogen-tag-supported peptide compounds. This auxiliary was easily installed on a variety of amino acids including oligopeptides that have a broad range of noncanonical residues, allowing simple purification of the products by crystallization and filtration. We demonstrated a de novo solid/hydrophobic-tag relay synthesis (STRS) strategy using the nitrogen-bound auxiliary for total synthesis of calpinactam.

Intermolecular Hydroalkoxylation and Hydrocarboxylation of 2-Azadienes with High Efficiency

Described here is a method for intermolecular hydroalkoxylation and hydrocarboxylation of 2-azadienes through cobalt-catalyzed hydrogen atom transfer and oxidation. This protocol provides a source of 2-azaallyl cation equivalents under mild conditions, is chemoselective in the presence of other C═C double bonds, and requires no excess amount of added alcohol or oxidant. Mechanistic studies suggest that the selectivity arises from lowering the transition state that leads to the highly stabilized 2-azaallyl radical.

Pd-catalyzed Ligand-Free ortho-Deuteration of Aromatic Carboxylic Acids with D2O

A ligand-free, palladium-catalyzed ortho-deuteration of aromatic carboxylic acid was developed using D2O as deuterium-source. Compared to their meta-substituted analogues, an unusually lower reactivity in para- and ortho-substituted benzoic acids toward hydrogen isotope exchange was observed. Further investigation revealed that the reaction temperature is a critical parameter for the reactivity, and the modified condition can afford deuterated products with good to excellent deuterium-incorporation.

Co-catalyzed C(sp3)−C(sp2) bond cleavage via hydrogen atom transfer

The discovery of a new Co-catalyzed hydrogen atom transfer (HAT) C(sp3)-C(sp2) bond cleavage method to access ketones from alkenes is reported. This unprecedented transformation features mild reaction conditions and good...