A computational study of the copper(II)-catalyzed enantioselective intramolecular aminooxygenation of alkenes

Study on Pyridine-Boryl Radical-Promoted, Ketyl Radical-Mediated Carbon-Carbon Bond-Forming Reactions

Ketyl radicals are synthetically versatile reactive species, but their applications have been hampered by harsh generation conditions employing highly reducing metals. Recently, the pyridine-boryl radical received wide attention as a promising organic reductant because of its mildness as well as convenience in handling. While probing the utility of the pyridine-boryl radical, our group observed facile pinacol coupling reactivity that had not been known at that time. This serendipitous finding was successfully rendered into a practical synthesis of tetraaryl-1,2-diols in up to 99% yield within 1 h. Subsequently, upon examinations of various reaction manifolds, a diastereoselective ketyl-olefin cyclization was accomplished to produce cycloalkanols such as trans-2-alkyl-1-indanols. Compared to the previous methods, the stereocontrolling ability was considerably enhanced by taking advantage of the structurally modifiable boryl group that would be present near the bond-forming site. In this full account, our synthetic efforts with the O-boryl ketyl radicals are disclosed in detail, covering the discovery, optimization, scope expansion, and mechanistic analysis, including density functional theory (DFT) calculations.

Stereochemical modulation of ketyl radical cyclization enabled by pyridine-boryl radicals: catalytic diastereoselective synthesis of trans-2-alkyl-1-indanols

Previously available ketyl radical cyclization conditions suffer from low and uncontrollable diastereoselectivity because of the absence of reagent-substrate interactions. In this report, stereochemical modulation was accomplished by taking advantage of the pyridine-boryl radical, which leaves the synthetically modifiable boronate moiety on the carbonyl oxygen near the reacting center during the stereo-determining cyclization step. In consequence, a catalytic diastereoselective synthesis of trans-2-substituted-1-indanols was achieved in the presence of a sterically congested six-membered diboronic ester and an efficient hydrogen atom donor.

Copper-Catalyzed Enantioselective Aerobic Alkene Aminooxygenation and Dioxygenation: Access to 2-Formyl Saturated Heterocycles and Unnatural Proline Derivatives

Alkene aminooxygenation and dioxygenation reactions that result in carbonyl products are uncommon, and protocols that control absolute stereochemistry are rare. We report herein catalytic enantioselective alkene aminooxygenation and dioxygenation that directly provide enantioenriched 2-formyl saturated heterocycles under aerobic conditions. Cyclization of substituted 4-pentenylsulfonamides, catalyzed by readily available chiral copper complexes and employing molecular oxygen as both oxygen source and stoichiometric oxidant, directly provides chiral 2-formyl pyrrolidines efficiently. Reductive or oxidative workup of these aldehydes provides their respective amino alcohols or amino acids (unnatural prolines). Enantioselective synthesis of an indoline and isoquinolines is also demonstrated. Concurrently, cyclization of various alkenols under similar conditions provides 2-formyl tetrahydrofurans, phthalans, isochromans, and morpholines. The nature of the copper ligands, the concentration of molecular oxygen, and the reaction temperature all impact the product distribution. Chiral nitrogen and oxygen heterocycles are common components of bioactive small molecules, and these enabling technologies provide access to saturated heterocycles functionalized with ready-to-use carbonyl electrophiles.

Stereoselective and Regioselective Synthesis of Heterocycles via Copper-Catalyzed Additions of Amine Derivatives and Alcohols to Alkenes

This Perspective describes the development of a family of copper(II)-catalyzed alkene difunctionalization reactions that enable stereoselective addition of amine derivatives and alcohols onto pendant unactivated alkenes to provide a range of valuable saturated nitrogen and oxygen heterocycles. 2-Vinylanilines and related substrates undergo alternative oxidative amination or allylic amination pathways, and these reactions will also be discussed. The involvement of both polar and radical steps in the reaction mechanisms have been implicated. Major product formation is a function of the lowest energy pathway, which in turn is a function of structural aspects of the various reaction components.

Direct Synthesis of 2-Formylpyrrolidines, 2-Pyrrolidinones and 2-Dihydrofuranones via Aerobic Copper-Catalyzed Aminooxygenation and Dioxygenation of 4-Pentenylsulfonamides and 4-Pentenylalcohols

A new method for the direct conversion of 4-pentenylsulfonamides to 2-formylpyrrolidines and a 2-ketopyrrolidine has been developed. This transformation occurs via aerobic copper-catalyzed alkene aminooxygenation where molecular oxygen serves as both oxidant and oxygen source. The 2-formylpyrrolidines can further undergo oxidative carbon-carbon bond cleavage in situ upon addition of DABCO, providing 2-pyrrolidinones. These transformations have been demonstrated for a range of 4-pentenylsulfonamides. 4-Pentenylalcohols also undergo oxidative cyclization to form γ-lactones predominantly. The reaction is chemoselective, oxidizing one alkene in the presence of others, and is compatible with several functional groups. Application of these reactions to the formal syntheses of baclofen and (+)-monomorine was demonstrated.

Copper-catalyzed oxidative carbon–heteroatom bond formation: a recent update

This review updates recent advances in Cu-catalyzed (anaerobic) oxidative carbon–heteroatom bond formation on sp³- and sp²-C–H bonds as well as alkenes, classified according to the types of stoichiometric oxidants.

Unique molecular geometries of reduced 4- and 5-coordinate zinc complexes stabilised by diiminopyridine ligand

Stepwise reduction of the diiminopyridine complex dimpyrZnCl₂ by KC₈ leads to compounds dimpyrZnCl (2), dimpyrZnCl(DMAP) (3) and dimpyrZn(DMAP)₂ (4) having unusual square-planar and see-saw geometries.

Copper-catalyzed radical cascade cyclization for the synthesis of phosphorated indolines

A novel and convenient approach to the synthesis of various phosphorated indolines via a copper-catalyzed radical cascade cyclization reaction has been developed.

6-Azabicyclo[3.2.1]octanes Via Copper-Catalyzed Enantioselective Alkene Carboamination

Bridged bicyclic rings containing nitrogen heterocycles are important motifs in bioactive small organic molecules. An enantioselective copper-catalyzed alkene carboamination reaction that creates bridged heterocycles is reported herein. Two new rings are formed in this alkene carboamination reaction where N-sulfonyl-2-aryl-4-pentenamines are converted to 6-azabicyclo[3.2.1]octanes using [Ph-Box-Cu](OTf)₂ or related catalysts in the presence of MnO₂ as stoichiometric oxidant in moderate to good yields and generally excellent enantioselectivities. Two new stereocenters are formed in the reaction, and the C-C bond-forming arene addition is a net C-H functionalization.

Copper-Catalyzed Alkene Diamination: Synthesis of Chiral 2-Aminomethyl Indolines and Pyrrolidines

Chiral vicinal diamines, including 2-aminomethyl indolines and pyrrolidines, are useful as ligands for catalytic asymmetric reactions and are also found as important components of bioactive compounds. Herein is reported the first copper-catalyzed alkene diamination that occurs with high enantioselectivity. The substrate range is the broadest yet reported for this kind of intra-/intermolecular reaction sequence both with respect to γ-alkenyl sulfonamide substrate and external amine nucleophile. The resulting products expand the availability of substituted 2-aminomethyl indolines and pyrrolidines, privileged compounds in asymmetric catalysis and medicinal chemistry. A unique solution to a challenging oxidation problem related to copper catalyst turnover is also presented.

DFT/TDDFT insights into the chemistry, biochemistry and photophysics of copper coordination compounds

Highlighting the recent progress in DFT/TDDFT application to coordination chemistry of copper.