Regio- and Enantioselective O-Allylation of Phenol and Alcohol Catalyzed by a Planar-Chiral Cyclopentadienyl Ruthenium Complex

Cobalt-Catalyzed Enantioselective Alkenylation of Aldehydes

Catalytic enantioselective alkenylation of aldehydes with easily accessible alkenyl halides promoted by a chiral cobalt complex derived from a newly developed tridentate bisoxazolinephosphine is presented. Such processes represent an unprecedented reaction pathway for cobalt catalysis and a general approach that enable rapid construction of highly diversified enantioenriched allylic alcohols containing a 1,1-, 1,2-disubstituted and trisubstituted alkene as well as axial stereogenicity in up to 99 % yield and 99 : 1 er without the need of preformation of alkenyl-metal reagents. DFT calculations revealed the origin of enantioselectivity.

Z-Retentive Asymmetric Allylic Substitution Reactions of Aldimine Esters under Ru/Cu Dual Catalysis

Ru/Cu dual catalysis has been applied for Z-retentive asymmetric allylic substitution reactions of aldimine esters. This reaction provides an enantioselective synthesis of chiral Z-olefins in high yields (up to 91% yield) with excellent enantioselectivity (up to 98% ee) under mild conditions. The previously unreacted trisubstituted allylic electrophiles under Ir catalytic system are found to be compatible, affording the stereoretentive products in either Z- or E-form. Both linear and branched allylic electrophiles are suitable substrates with excellent reaction outcomes. Notably, Ru and Cu complexes are added in one-pot and simplifies the manipulation of this protocol and self-sorting phenomena could be observed in this Ru/Cu dual catalytic system.

Synthesis, stereochemical assignment, and enantioselective catalytic activity of late transition metal planar chiral complexes

Planar chirality is an important form of molecular chirality that can be utilized to induce enantioselectivity when incorporated into transition metal catalysts. However, due to synthetic constraints, the use of late transition metal planar chiral complexes to conduct enantioselective transformations has been limited. Additionally, the published methods surrounding the stereochemical assignment of planar chiral compounds are sometimes conflicting, making proper assignment difficult. This review aims to provide clarity on the methods available to assign planar chirality and provide an overview on the synthesis and use of late transition metal planar chiral complexes as enantioselective catalysts.

Migratory allylic arylation of 1,n-enols enabled by nickel catalysis

Transition-metal-catalyzed allylic substitution reactions (Tsuji-Trost reactions) proceeding via a π-allyl metal intermediate have been demonstrated as a powerful tool in synthetic chemistry. Herein, we disclose an unprecedented π-allyl metal species migration, walking on the carbon chain involving 1,4-hydride shift as confirmed by deuterium labeling experiments. This migratory allylic arylation can be realized under dual catalysis of nickel and lanthanide triflate, a Lewis acid. Olefin migration has been observed to preferentially occur with the substrate of 1,n-enols (n ≥ 3). The robust nature of the allylic substitution strategy is reflected by a broad scope of substrates with the control of regio- and stereoselectivity. DFT studies suggest that π-allyl metal species migration consists of the sequential β-H elimination and migratory insertion, with diene not being allowed to release from the metal center before producing a new π-allyl nickel species.

Palladium-Catalyzed Regioselective Intermolecular Hydroalkoxylation of 1-Arylbutadienes

An efficient method for the synthesis of (E)-(3-alkoxybut-1-enyl)benzenes by Pd-catalyzed regioselective intermolecular hydroalkoxylation of 1-arylbutadienes has been developed. This method can be executed in a simple operation with no dry reaction conditions required and having tolerance to a wide range of substrates. Chloromethyl methyl ether (MOMCl) as an additive was found to be essential for the success of the reaction.

Palladium-Catalyzed Decarboxylative O-Allylation of Phenols with γ-Methylidene-δ-valerolactones

A novel Palladium-Catalyzed decarboxylative O-allylation of phenols was developed, in which a γ-methylidene-δ- valerolactone (GMDVs) was found to be an efficient and selective allylation reagent, affording the target allyl phenyl...

Nickel/Brønsted acid dual-catalyzed regioselective C–H bond allylation of phenols with 1,3-dienes

A nickel/Brønsted acid dual-catalyzed C-H bond ortho-allylation of phenols with 1,3-dienes has been developed. This methodology is readily applicable to the modification of complex pharmaceutical molecules.

Enantio- and regioselective asymmetric allylic substitution using a chiral aminophosphinite ruthenium complex: an experimental and theoretical investigation

The design and synthesis of a new chiral aminophosphinite-ligated ruthenium complex is described. The ruthenium complex, [Ru(AMP)₂(CH₃CN)₂][BPh₄]₂ {AMP = (S)-tert-butyl 1-(diphenylphosphinooxy)-3-methylbutan-2-ylcarbamate}, has been found to catalyze nucleophilic addition of phenol and carboxylic acid to allyl chloride in a highly regioselective fashion with enantiomeric excess ranging from 12 to 90.

Palladium-Catalyzed Cascade Allylative Dicarbofunctionalization of Aryl Phenol-Tethered Alkynes with Allyl Iodides: Synthesis of Skipped Dienes

A palladium-catalyzed cascade allylative dicarbofunctionalization of aryl phenol-tethered alkynes with allyl iodides is described. A series of polysubstituted spirocyclo-containing skipped dienes with an all-carbon tetrasubstituted alkene unit are synthesized through this convenient process. The cascade reaction proceeds selectively through dearomative C-allylation instead of O-allylation of aryl phenols.

Transition-metal-catalyzed ortho-selective C-H functionalization reactions of free phenols

Phenols are important readily available chemical feedstocks and versatile synthetic building blocks for diverse synthetic transformations. Their motifs are prevalent in a diverse array of natural products, pharmaceuticals, functional materials, and privileged chiral ligands. Consequently, the development of facile and direct site-selective C-H bond functionalization of free phenols is of great importance and considerable interest to both industry and academic research. Over the past decades, transition-metal-catalyzed C-H bond functionalization has become as a powerful synthetic tool in organic synthesis. In this review, we provide a brief overview of recent progress in the transition-metal-catalyzed direct ortho-selective C-H functionalization of free phenols.

Rhodium(i)/bisoxazolinephosphine-catalyzed regio- and enantioselective amination of allylic carbonates: a computational study

DFT calculations were performed to investigate the rhodium(i)/bisoxazolinephosphine-catalyzed regio- and enantioselective amination of allylic carbonates.

Ruthenium-Catalyzed Asymmetric Allylic Alkylation of Isatins

A new ruthenium-based catalytic system for branched-selective asymmetric allylic alkylation is disclosed and applied to the synthesis of chiral isatin derivatives. The catalyst, which is generated in situ from commercially available CpRu(MeCN)₃PF₆ and a BINOL-derived phosphoramidite, is both highly active (TON up to 180) and insensitive to air and moisture. Additionally, the N-alkylated isatins accessible using this methodology are versatile building blocks that are readily transformed into chiral analogs of achiral drug molecules.

Synthesis of an optically active polymer containing a planar phthalimide backbone by asymmetric polymerization

Herein we present the precise design and synthesis of a novel polymer backbone that induces a helical structure through asymmetric polymerization reactions of a phthalimide-based monomer catalyzed by a planar-chiral cyclopentadienyl–ruthenium complex.

Iridium-Catalyzed Asymmetric Allylic Substitution Reactions

In this review, we summarize the origin and advancements of iridium-catalyzed asymmetric allylic substitution reactions during the past two decades. Since the first report in 1997, Ir-catalyzed asymmetric allylic substitution reactions have attracted intense attention due to their exceptionally high regio- and enantioselectivities. Ir-catalyzed asymmetric allylic substitution reactions have been significantly developed in recent years in many respects, including ligand development, mechanistic understanding, substrate scope, and application in the synthesis of complex functional molecules. In this review, an explicit outline of ligands, mechanism, scope of nucleophiles, and applications is presented.

Catalytic, Enantioselective, Intramolecular Sulfenofunctionalization of Alkenes with Phenols

The catalytic, enantioselective, cyclization of phenols with electrophilic sulfenophthalimides onto isolated or conjugated alkenes affords 2,3-disubstituted benzopyrans and benzoxepins. The reaction is catalyzed by a BINAM-based phosphoramide Lewis base catalyst which assists in the highly enantioselective formation of a thiiranium ion intermediate. The influence of nucleophile electron density, alkene substitution pattern, tether length and Lewis base functional groups on the rate, enantio- and site-selectivity for the cyclization is investigated. The reaction is not affected by the presence of substituents on the phenol ring. In contrast, substitutions around the alkene strongly affect the reaction outcome. Sequential lengthening of the tether results in decreased reactivity, which necessitated increased temperatures for reaction to occur. Sterically bulky aryl groups on the sulfenyl moiety prevented erosion of enantiomeric composition at these elevated temperatures. Alcohols and carboxylic acids preferentially captured thiiranium ions in competition with phenolic hydroxyl groups. An improved method for the selective C(2) allylation of phenols is also described.

Development of a Coordinatively Unsaturated Chiral Indenylruthenium Catalyst

An unprecedented coordinatively unsaturated chiral indenylruthenium complex 12 was designed and synthesized to provide additional coordination sites for Ru-catalyzed asymmetric transformations. In an attempt to catalyze an asymmetric enyne cycloisomerization reaction of 1,6-enyne, significant amounts of hydroxycyclization were observed. Up to 84:16 er of the hydroxycyclization product was obtained in 2-MeTHF. This chiral indenylruthenium catalyst could also perform an asymmetric redox isomerization/C-H insertion reaction in up to 90:10 er.

Chiral cyclopentadienylruthenium sulfoxide catalysts for asymmetric redox bicycloisomerization

A full account of our efforts toward an asymmetric redox bicycloisomerization reaction is presented in this article. Cyclopentadienylruthenium (CpRu) complexes containing tethered chiral sulfoxides were synthesized via an oxidative [3 + 2] cycloaddition reaction between an alkyne and an allylruthenium complex. Sulfoxide complex 1 containing a p-anisole moiety on its sulfoxide proved to be the most efficient and selective catalyst for the asymmetric redox bicycloisomerization of 1,6- and 1,7-enynes. This complex was used to synthesize a broad array of [3.1.0] and [4.1.0] bicycles. Sulfonamide- and phosphoramidate-containing products could be deprotected under reducing conditions. Catalysis performed with enantiomerically enriched propargyl alcohols revealed a matched/mismatched effect that was strongly dependent on the nature of the solvent.

Iterative catalyst controlled diastereodivergent synthesis of polypropionates

Polypropionates are synthesized using a combination of a copper-catalyzed asymmetric allylic alkylation, ruthenium-catalyzed cross-metathesis and iridium-catalyzed asymmetric allylic etherification.

Enantio- and diastereoselective polymerization: asymmetric allylic alkylation catalyzed by a planar-chiral Cp′Ru complex

In this study, we examined the regio-, diastereo-, and enantioselective polymerization using asymmetric allylic alkylation catalyzed by a planar-chiral cyclopentadienyl-ruthenium (Cp′Ru) complex ((S)-1).

Pincer-Nickel-Catalyzed Allyl-Aryl Coupling between Allyl Methyl Ethers and Arylzinc Chlorides

The P,N,N-pincer nickel complex [Ni(Cl){N(2-Ph2PC6H4)(2'-Me2NC6H4)}]-catalyzed allyl-aryl coupling was studied. The reaction of allyl methyl ethers, including (1-methoxyallyl)arenes and (3-methoxyprop-1-en-1-yl)arenes, with arylzinc chlorides afforded linear (E)-alkenes in high yields, whereas the reaction of (E)-1-methoxytridec-2-ene with p-Me2NC6H4ZnCl generated a mixture of linear and branched alkenes.

Chirality Transfer in Gold(I)-Catalysed Direct Allylic Etherifications of Unactivated Alcohols: Experimental and Computational Study

Gold(I)-catalysed direct allylic etherifications have been successfully carried out with chirality transfer to yield enantioenriched, γ-substituted secondary allylic ethers. Our investigations include a full substrate-scope screen to ascertain substituent effects on the regioselectivity, stereoselectivity and efficiency of chirality transfer, as well as control experiments to elucidate the mechanistic subtleties of the chirality-transfer process. Crucially, addition of molecular sieves was found to be necessary to ensure efficient and general chirality transfer. Computational studies suggest that the efficiency of chirality transfer is linked to the aggregation of the alcohol nucleophile around the reactive π-bound Au-allylic ether complex. With a single alcohol nucleophile, a high degree of chirality transfer is predicted. However, if three alcohols are present, alternative proton transfer chain mechanisms that erode the efficiency of chirality transfer become competitive.

Dehydrative thiolation of allenols: indium vs gold catalysis

Intermolecular additions of thiols to allenols via formal S(N)2' selectivity to produce functionalized dienes are described. Although this dehydrative reaction was initially developed using gold(I) catalysis, indium(III) proves to be a far superior catalyst in terms of selectivity and substrate scope.

Enantio- and diastereoselective asymmetric allylic alkylation catalyzed by a planar-chiral cyclopentadienyl ruthenium complex

We report asymmetric allylic alkylation of allylic chloride with β-diketones as the prochiral carbon nucleophiles using a planar-chiral Cp′Ru catalyst.

Enantioselective synthesis of 4-substituted tetrahydroisoquinolines via palladium-catalyzed intramolecular Friedel–Crafts type allylic alkylation of phenols

Pd-catalyzed asymmetric intramolecular allylic alkylation reaction of phenols was developed, affording C4 substituted tetrahydroisoquinolines in moderate to excellent yields, enantioselectivity and regioselectivity.

Gold(I)-catalysed direct thioetherifications using allylic alcohols: an experimental and computational study

A gold(I)-catalysed direct thioetherification reaction between allylic alcohols and thiols is presented. The reaction is generally highly regioselective (S(N)2'). This dehydrative allylation procedure is very mild and atom economical, producing only water as the by-product and avoiding any unnecessary waste/steps associated with installing a leaving or activating group on the substrate. Computational studies are presented to gain insight into the mechanism of the reaction. Calculations indicate that the regioselectivity is under equilibrium control and is ultimately dictated by the thermodynamic stability of the products.

A multitasking functional group leads to structural diversity using designer C-H activation reaction cascades

The C-H activation strategy has become one of the preferred methods to introduce chemical functionality to a chemically inert carbon atom. Intensive efforts have been devoted to developing either versatile bond formations (product structural diversity) or effective directing groups (substrate site selectivity). From the views of medicinal and synthetic practitioners, the C-H activation approach remains inadequate due to its limitation to point-to-point derivatization. Direct assembly of 3D molecular complexity in a single step remains elusive for this strategy. Towards this goal, a multitasking functional group is required to accomplish several missions in one pot: site selecitivity, cleavability and redox versatility. We demonstrate that an oxyacetamide group is such a multifunctional warhead that enables a series of C-H functionalization cascades and allows direct access to structurally diverse polycyclic heterocyles in one pot. The progress of these reaction cascades were fully controlled by oxidants and temperature. The proliferation of the reaction chain can be extended to a four-step cascade.