Iminophenyl Oxazolinylphenylamine for Enantioselective Cobalt-Catalyzed Hydrosilylation of Aryl Ketones

A new family of chiral iminophenyl oxazolinyl­phenylamines (IPOPA) was designed and synthesized through three steps from commercially available starting materials. An efficient cobalt-catalyzed asymmetric hydrosilylation of simple ketones with a low catalyst loading of CoCl₂ and IPOPA was developed to afford chiral alcohols in good yields with high enantioselectivities

Dual-Stereocontrol Asymmetric Cobalt-Catalyzed Hydroboration of Sterically Hindered Styrenes

An oxazoline aminoisopropylpyridine (OAP) was designed and synthesized for cobalt-catalyzed asymmetric hydroboration of sterically hindered styrenes. A unique dual-stereocontrol phenomenon was observed using a rigid OIP·CoCl₂ complex or a flexible OAP with CoCl₂ as precatalysts, respectively. The reaction could be easily carried out on a gram scale to afford chiral alkylboronic esters which could be converted into diverse C–X (X = C, N, O) bond cross-coupling products. The mechanistically distinct pathways were proposed on the basis of deuterium experiments

Cobalt-Catalyzed Ligand-Controlled Regioselective Hydroboration/Cyclization of 1,6-Enynes

A ligand-controlled cobalt-catalyzed regioselective hydroboration/cyclization of 1,6-enynes with HBPin was developed by switching the size of the coordinated side arm to afford alkenylboronates and alkylboronates, respectively. Gram-scale reactions could be easily conducted, which is beneficial for further derivatizations. A primary mechanism was proposed on the basis of substrate-controlled experiments and deuterium experiments

Dual-Stereocontrol Asymmetric Cobalt-Catalyzed Hydroboration of Sterically Hindered Styrenes

An oxazoline aminoisopropylpyridine (OAP) was designed and synthesized for cobalt-catalyzed asymmetric hydroboration of sterically hindered styrenes. A unique dual-stereocontrol phenomenon was observed using a rigid OIP·CoCl₂ complex or a flexible OAP with CoCl₂ as precatalysts, respectively. The reaction could be easily carried out on a gram scale to afford chiral alkylboronic esters which could be converted into diverse C–X (X = C, N, O) bond cross-coupling products. The mechanistically distinct pathways were proposed on the basis of deuterium experiments

Intermolecular [2 + 2] Cycloaddition of 1,4-Dihydropyridines with Olefins via Energy Transfer

A highly regio- and diastereoselective visible-light-promoted [2 + 2] cycloaddition between readily available 1,4-dihydropyridines and olefins has been developed. This strategy is operationally simple and atom-economical and enables the construction of strained polysubstituted 2-azabicyclo[4.2.0]­octanes with three all-carbon quaternary centers with good functional group tolerance. These products can be easily converted to various structurally unique derivatives. The primary mechanistic studies demonstrated that the reaction proceeds through an energy transfer pathway

Cobalt-Catalyzed Hydrosilylation/Cyclization of 1,6-Enynes

An iminopyridine cobalt dichloride complex was synthesized and demonstrated as an effective precatalyst for hydrosilylation/cyclization of 1,6-enynes with silanes. Various functional groups such as amine, free aniline, ester, ether, cyano, halide, trifluoromethyl, and heterocycle were tolerated to afford a variety of silicon-containing compounds. The reaction could be scaled up to afford products on the gram scale which could undergo further derivatizations. A primary mechanism was proposed based on analysis of side products and a deuterated experiment

Intermolecular [2 + 2] Cycloaddition of 1,4-Dihydropyridines with Olefins via Energy Transfer

A highly regio- and diastereoselective visible-light-promoted [2 + 2] cycloaddition between readily available 1,4-dihydropyridines and olefins has been developed. This strategy is operationally simple and atom-economical and enables the construction of strained polysubstituted 2-azabicyclo[4.2.0]­octanes with three all-carbon quaternary centers with good functional group tolerance. These products can be easily converted to various structurally unique derivatives. The primary mechanistic studies demonstrated that the reaction proceeds through an energy transfer pathway

Visible-Light-Promoted Oxidative [4 + 2] Cycloadditions of Aryl Silyl Enol Ethers

Visible-light-promoted oxidative [4 + 2] cycloadditions of ε,3-unsaturated silyl enol ethers have been developed to efficiently and diastereoselectively construct polycyclic skeletons under mild conditions. The diastereoselectivities were dependent on the stereoconfiguration of silyl enol ether, substitutions on the link, as well as electric properties of substitutions on aryl rings. The intermediates could be trapped by TEMPO, oxygen or methanol. Mechanistic studies indicated the reaction was initiated by one-electron oxidation of the silyl enol ether

Intramolecular Pd(II)-Catalyzed Aerobic Oxidative Amination of Alkenes: Synthesis of Six-Membered <i>N</i>-Heterocycles

Use of a base-free Pd(DMSO)₂(TFA)₂ catalyst system enables the synthesis of six-membered nitrogen heterocycles via a Wacker-type aerobic oxidative cyclization of alkenes bearing tethered sulfonamides. Various heterocycles, including morpholines, piperidines, piperazines, and piperazinones, are accessible by this method

Palladium-Catalyzed C‑2 C–H Heteroarylation of Chiral Oxazolines: Diverse Synthesis of Chiral Oxazoline Ligands

A direct, efficient, and practical protocol to install a chiral oxazoline unit onto aryl/heteroaryl rings via palladium-catalyzed C–H functionalization of 2-positions of oxazolines with a variety of halides using dppe as the ligand has been developed. Various chiral oxazoline ligands could be synthesized, even in a 10-g scale process. This protocol is a good supplement to traditional methods and for diverse synthesis of chiral oxazoline ligands