Oxidative Dehydrogenation of Alkanes through Homogeneous Base Metal Catalysis.

Preparing valuable olefins from cheap and abundant alkane resources has long been a challenging task in organic synthesis, which mainly suffers from harsh reaction conditions and narrow scopes. Homogeneous transition metals catalyzed dehydrogenation of alkanes has attracted much attention for its excellent catalytic activities under relatively milder conditions. Among them, base metal catalyzed oxidative alkane dehydrogenation has emerged as a viable strategy for olefin synthesis for its usage of cheap catalysts, compatibility with various functional groups, and low reaction temperature.

Catalytic S Ar Hexafluoroisopropoxylation of Aryl Chlorides and Bromides.

Fluoroalkyl aryl ethers are valuable structural motifs in pharmaceuticals because compounds with these motifs are more metabolically stable and more lipophilic than their nonfluorinated analogues. However, hexafluoroisopropyl aryl ethers have not been extensively studied, presumably because of the lack of efficient synthetic methods. Herein, we describe a rhodium-catalyzed nucleophilic aromatic substitution of aryl chlorides or bromides, which act as the limiting reagents, with weakly nucleophilic hexafluoro-2-propanol under mild reaction conditions.

Rhodium-Catalyzed Benzylic Addition Reactions of Alkylarenes to Michael Acceptors.

The use of alkylarenes as nucleophile precursors in benzylic addition is challenging because the benzylic hydrogen atoms of these compounds are inert to deprotonation. Herein, we report Rh-catalyzed benzylic addition of alkylarenes to Michael acceptors for the formation of C(sp )-C(sp ) bonds. The catalyst is proposed to activate the aromatic ring via η -coordination, dramatically facilitating deprotonation of the unactivated benzylic C-H bond and addition of the resulting carbanion to the α,β-unsaturated double bond in the absence of bases.

Catalytic Amination of Phenols with Amines.

Given the wide prevalence and ready availability of both phenols and amines, aniline synthesis through direct coupling between these starting materials would be extremely attractive. Herein, we describe a rhodium-catalyzed amination of phenols, which provides concise access to diverse anilines, with water as the sole byproduct. The arenophilic rhodium catalyst facilitates the inherently difficult keto-enol tautomerization of phenols by means of π-coordination, allowing for the subsequent dehydrative condensation with amines.

Rhodium-Catalyzed Stereoselective Deuteration of Benzylic C-H Bonds via Reversible η -Coordination.

We report a convenient method for benzylic H/D exchange of a wide variety of substrates bearing primary, secondary, or tertiary C-H bonds via a reversible η -coordination strategy. A doubly cationic [Cp Rh ] catalyst that serves as an arenophile facilitates deprotonation of inert benzylic hydrogen atoms (pK >40 in DMSO) without affecting other hydrogen atoms, such as those on aromatic rings or in α-positions of carboxylate groups. Notably, the H/D exchange reactions feature high stereoretention.

Catalytic S Ar Hydroxylation and Alkoxylation of Aryl Fluorides.

Nucleophilic aromatic substitution (S Ar) is a powerful strategy for incorporating a heteroatom into an aromatic ring by displacement of a leaving group with a nucleophile, but this method is limited to electron-deficient arenes. We have now established a reliable method for accessing phenols and phenyl alkyl ethers via catalytic S Ar reactions. The method is applicable to a broad array of electron-rich and neutral aryl fluorides, which are inert under classical S Ar conditions.

Ru(II)-Catalyzed Amination of Aryl Fluorides η-Coordination.

We developed a Ru/hemilabile-ligand-catalyzed nucleophilic aromatic substitution (SAr) of aryl fluorides as the limiting reagents. Significant ligand enhancement was demonstrated by the engagement of both electron-rich and neutral arenes in the SAr amination without using excess arenes. Preliminary mechanistic studies revealed that the nucleophilic substitution proceeds on a η-complex of the Ru catalyst and the substrate, and the hemilabile ligand facilitates dissociation of products from the metal center.

Asymmetric Synthesis of α-Amino Acids by Organocatalytic Biomimetic Transamination.

A biomimetic enantioselective transamination of α-keto ester derivatives can be realized under mild conditions by using chiral quaternary ammonium arenecarboxylates in the absence of base additives. The corresponding α-amino acids can be used as versatile intermediates for further synthetic transformations that furnish chiral pyrrolidine and octahydroindolizine derivatives.

Enantioselective Alkylation of N-Arylhydrazones Derived from α-Keto Esters and Isatin Derivatives through Asymmetric Phase-Transfer Catalysis.

The phase-transfer-catalyzed asymmetric alkylation reactions of N-arylhydrazones derived from α-keto-esters and isatin derivatives afford enantioenriched azo compounds that bear a tetra-substituted carbon stereocenter in good yields with high chemo- and enantioselectivity. The alkylation products can be readily converted into chiral amino esters, hydrazine derivatives, and aza-β-lactams without loss of enantiopurity.

Cy-SaBOX/Copper(II)-Catalyzed Highly Diastereo- and Enantioselective Synthesis of Bicyclic N,O Acetals.

Facile and effective access for the asymmetric construction of the useful and important skeleton of the bicyclic N,O-acetals is described. Cu(II) /SaBOX could catalyze the reaction of β,γ-unsaturated α-ketoesters with cyclic enamines efficiently, thus affording the desired products in excellent yields with excellent stereoselectivities (21 examples; up to 99 % yields; up to >95:5 d.r.

Asymmetric H2O-Nucleophilic Ring Opening of D-A Cyclopropanes: Catalyst Serves as a Source of Water.

The first catalytic enantioselective ring-opening reaction of donor-acceptor cyclopropanes with water is described. By employing Cy-TOX/Cu(II) as catalyst, the reaction performed very well over a broad range of substrates, leading to the ring-opening products in 70-96% yields with up to 95% ee under mild conditions. The current method provides a new approach to direct access to γ-substituted GBH derivatives very efficiently.