Chiral Cyclic Ligand-Enabled Iridium-Catalyzed Asymmetric Arylation of Unactivated Racemic Allylic Alcohols with Anilines

Development of Diverse Ligands and Catalysts Derived from Axially Chiral Cyclic Biphenyldiols

The development of suitable chiral ligands and catalysts is a key factor in asymmetric organic synthesis. In this paper, we describe the design, synthesis and evaluation of a new kind of adjustable axially chiral cyclic biphenyl ligands and catalysts derived from axially chiral cyclic biphenyldiols, and four representative examples were performed well including enantioselective alkynylation of benzo[e][1,2,3]oxathiazine 2,2-dioxide under catalysis of (R)-cyclic [1,1'-biphenyl]-2,2'-diol/ZnMe2, palladium-catalyzed decarboxylative cycloaddition of 4-phenyl-4-vinyl-1,3-dioxolan-2-one with 2-arylidenemalononitriles in the presence of axially chiral cyclic phosphoramidite ligand, and axially chiral cyclic phosphoric acid-catalyzed asymmetric Diels-Alder cycloaddition of styryl-1H-indole with cyclic 2,4-dienones and asymmetric Michael addition of indolizine to cyclopentenediones. The experiments showed that variation of 2,2'-substituent groups could provide different kinds of axially chiral cyclic ligands and catalysts, variation of steric and electronic properties (by changing substituent groups at the 3,3',5,5'-positions) and dihedral angles (by changing ring sizes at 6,6'-positions) could greatly change catalytic efficiency of ligands and catalysts derived from axially chiral cyclic biphenyldiols. The high reactivity and stereoselectivity of the reactions were effectively achieved through the precise regulation of multi-sites on our axially chiral cyclic biphenyldiols.

Catalytic Enantioselective Friedel-Crafts Allenylation

The first enantioselective Friedel-Crafts (FC) allenylation reaction for the creation of central chirality is developed under cooperative Ir(I)/(phosphoramidite,olefin) and Lewis acid catalysis. This enantioconvergent reaction utilizes racemic allenylic alcohol as the electrophile and shows compatibility with a variety of electron-rich arenes and heteroarenes. The resulting highly enantioenriched (up to >99.5 : 0.5 e.r.) 1,1-disubstituted allenylic methanes, bearing a benzylic carbon stereocenter, are obtained with complete regiocontrol - both on (hetero)arenes as well as on the allenylic fragment. This protocol allows for the enantioselective formal introduction of a 4-carbon alkyl chain into (hetero)arenes, along with the creation of a benzylic stereocenter. Judicious synthetic elaborations not only lead to formal enantioselective FC alkylation products of less electron-rich arenes but also of substituted arenes in ortho- and even meta-selective fashion. An intramolecular version of this FC allenylation is shown to proceed with promising enantioselectivity under the same catalytic conditions. Mechanistic studies revealed the involvement of dynamic kinetic asymmetric transformation (DyKAT) of racemic allenylic alcohols in this reaction.

Hydroxy-directed iridium-catalyzed enantioselective formal β-C(sp2)-H allylic alkylation of α,β-unsaturated carbonyls

Hydroxy-directed iridium-catalyzed enantioselective formal β-C(sp2)-H allylic alkylation of kojic acid and structurally related α,β-unsaturated carbonyl compounds is developed. This reaction, catalyzed by an Ir(i)/(P,olefin) complex, utilizes the nucleophilic character of α-hydroxy α,β-unsaturated carbonyls, to introduce an allyl group at its β-position in a branched-selective manner in good to excellent yield with uniformly high enantioselectivity (up to >99.9 : 0.1 er). To the best of our knowledge, this report represents the first example of the use of kojic acid in a transition metal catalyzed highly enantioselective transformation.

Synthesis of allylanilines via scandium-catalysed benzylic C(sp3)-H alkenylation with alkynes

The ortho-selective benzylic C(sp³)-H alkenylation of 2-methyl tertiary anilines with internal alkynes has been achieved for the first time by using a half-sandwich scandium catalyst. This protocol provides a straightforward route for the synthesis of a new family of 2-allylaniline derivatives, featuring broad substrate scope, 100% atom-efficiency, high yields, and high chemo-, regio-, and stereoselectivity.

Base-Promoted Cobalt-Catalyzed Regio- and Enantioselective para-Friedel-Crafts Alkylation of Aniline Derivatives

Herein we disclose a highly efficient enantioselective para-C-H alkylation of aniline derivatives promoted by a base/Co/indeno-pybox ligand system. This methodology leads to the efficient construction of a series of enantioenriched aniline derivatives bearing all-carbon quaternary stereocenters. In addition, several special biologically or medicinally active indoles are facilely synthesized by our Co-catalyzed asymmetry synthesis method. Density functional theory calculations and experiment results suggest that the (acac)^- anion of Co(acac)₂ plays a very important role in chiral control during the nucleophilic reaction.

Iridium(III) Catalyzed Z-Selective Allylic Arylation of α-Fluoro But-1-enoic Acid Amides via β-F-Elimination in Water

Allylic arylation of α-fluoro but-1-enoic acid amides with arylboronic acids was carried out in water by comparing the catalytic activity of iridium(III) and rhodium(III). Ir(III) has shown a strong superiority over Rh(III) to give allyl-aryl coupling products with excellent stereoselectivity in favor of the Z-isomer. The origin of high stereoselectivity is perhaps because of the a coordination of iridium Ir-N or Ir-O.

Synthesis of C5-Allylindoles through an Iridium-Catalyzed Asymmetric Allylic Substitution/Oxidation Reaction Sequence of N-Alkyl Indolines

Iridium/Brønsted acid cooperative catalyzed asymmetric allylic substitution reactions at the C5 position of indolines have been reported for the first time. The highly efficient protocol allows rapid access to various C5-allylated products in good to high yields (48-97%) and enantioselectivities (82% to >99% ee) with wide functional group tolerance. The transformations allow not only the formation of C5-allylindoline derivatives but also the synthesis of C5-allylindole analogues in good yields and excellent stereoselectivities via an allylation/oxidation reaction sequence.

Iridium-catalyzed enantioselective olefinic C(sp2)-H allylic alkylation

The first iridium-catalyzed enantioselective olefinic C(sp2)-H allylic alkylation is developed in cooperation with Lewis base catalysis. This reaction, catalyzed by cinchonidine and an in situ generated cyclometalated Ir(i)/phosphoramidite complex, makes use of the latent enolate character of an α,β-unsaturated carbonyl compound, namely coumalate ester, to introduce an allyl group at its α-position in a branched-selective manner in moderate to good yield with good to excellent enantioselectivities (up to 98 : 2 er).

Iridium-catalyzed intramolecular asymmetric allylic etherification of salicylic acid derivatives with chiral-bridged biphenyl phosphoramidite ligands

Iridium-catalyzed intramolecular asymmetric allylic etherification of salicylic acid derivatives was successfully realized for the first time.

Sulfonate N-Heterocyclic Carbene-Copper Complexes: Uniquely Effective Catalysts for Enantioselective Synthesis of C-C, C-B, C-H, and C-Si Bonds

A copper-based complex that contains a sulfonate N-heterocyclic carbene ligand was first reported 15 years ago. Since then, these organometallic entities have proven to be uniquely effective in catalyzing an assortment of enantioselective transformations, including allylic substitutions, conjugate additions, proto-boryl additions to alkenes, boryl and silyl substitutions, hydride-allyl additions to alkenyl boronates, and additions of boron-containing allyl moieties to N-H ketimines. In this review article, we detail the shortcomings in the state-of-the-art that fueled the development of this air stable ligand class, members of which can be prepared on multigram scale. For each reaction type, when relevant, the prior art at the time of the advance involving sulfonate NHC-Cu catalysts and/or subsequent key developments are briefly analyzed, and the relevance of the advance to efficient and enantioselective total or formal synthesis of biologically active molecules is underscored. Mechanistic analysis of the structural attributes of sulfonate NHC-Cu catalysts that are responsible for their ability to facilitate transformations with high efficiency as well as regio- and enantioselectivity are detailed. This review contains several formerly undisclosed methodological advances and mechanistic analyses, the latter of which constitute a revision of previously reported proposals.

Friedel-Crafts alkylation with α-bromoarylacetates for the preparation of enantioenriched 2,2-diarylethanols

Highly enantioenriched 2,2-diarylethanols can be efficiently synthesized through the Friedel-Crafts alkylation of (hetero)arenes with configurationally labile α-bromoarylacetates. The substitution of highly diastereoenriched α-bromoarylacetates occurs in the presence of AgOTf, and the subsequent reduction affords diverse 2,2-diarylethanols with high yields and enantioselectivities up to 99 : 1 er. In addition, the application of this asymmetric synthetic methodology to the preparation of highly enantioenriched dihydrobenzofuran and indoline derivatives is demonstrated.

Iridium-catalyzed intramolecular enantioselective allylation of quinazolin-4(3H)-one derivatives

An efficient chiral cyclic phosphoramidite ligand-enabled iridium-catalyzed intramolecular allylation of quinazolin-4(3H)-one derivatives has been developed with high reactivity and high to excellent enantioselectivity.

Iridium and a Brønsted acid cooperatively catalyzed chemodivergent and stereoselective reactions of vinyl benzoxazinones with azlactones

Under cooperative catalysis of iridium and a Brønsted acid, different C4-substituted azlactones react with vinyl benzoxazinones via a formal [4+2] cycloaddition or substitution reaction in a chemo- and stereoselective mode.

A concise construction of 4-alkynylquinazolines via [4 + 2] annulation of 4-alkynylbenzoxazinanones with acylhydroxamates under transition-metal-free conditions

A concise and highly efficient method for the construction of valuable 4-alkynylquinazolines under transition-metal-free conditions was developed via [4 + 2] annulation of 4-alkynylbenzoxazinanones with acylhydroxamates in good to excellent yields.

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.

Axially Chiral Cyclic Diphosphine Ligand-Enabled Palladium-Catalyzed Intramolecular Asymmetric Hydroarylation

In transition metal-catalyzed asymmetric synthesis, enantioselectivity strongly depends on the structures of chiral ligands, so the development of new chiral ligands is crucial. Here, an efficient and highly enantioselective palladium-catalyzed intramolecular hydroarylation has been developed, and a new kind of N-heterocycles, 1H-pyrazolo[5,1-a]isoindol-2(8H)-ones containing a quaternary stereocenter, was prepared in high yields and excellent enantiomeric excess values. The reaction was effectively catalyzed by palladium-diphosphine complexes with numerous functional group tolerance, in which the newly developed axially chiral cyclic diphosphine ligands played key roles in the reactivity and enantioselectivity of the substrates. We believe that the cyclic diphosphine ligands with adjustable dihedral angles will find wide application in asymmetric synthesis.

Enantioselective synthesis of gem-diarylalkanes by transition metal-catalyzed asymmetric arylations (TMCAAr)

To date, enantiomerically enriched molecules containing gem(1,1)-diaryl containing tertiary or quaternary stereogenic centers have been readily accessed by transition metal-catalyzed enantioselective or stereoconvergent aryl transfer reactions.

Chiral gem(1,1)-diaryl containing tertiary or quaternary stereogenic centers are present in many natural products and important pharmacophores. While numerous catalytic asymmetric methods enable access to 1,1-diaryl motifs, transition metal-catalyzed asymmetric arylations (TMCAAr) are one of the most powerful methods to prepare enantiopure gem-diarylalkane compounds. The main methodology includes enantioselective 1,2- or 1,4-additions across C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O, C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N and C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds by arylmetallic reagents; aryl cross-couplings of olefins, benzylic (pseudo)halides and aziridines; asymmetric aryl substitution reactions of allylic substrates; and isotopic benzylic C–H arylation.

Regio and Enantioselective Organocatalytic Friedel-Crafts Alkylation of 4-Aminoindoles at the C7-Position

A chiral phosphoric acid catalyzed highly regio- and enantioselective Friedel-Crafts alkylation at the indole C7-position was developed via the introduction of an alkylamine moiety at the C4-position of the indole ring. The methodology is applicable to a wide range of 4-aminoindoles and β,γ-unsaturated α-ketimino esters to furnish the corresponding C7-position functionalized chiral indole derivatives in high yields with moderate to excellent enantioselectivities. Furthermore, the α-ketimino ester moiety in the products is a versatile building block and enables many further transformations.

Alkylarylation of styrenes via direct C(sp3)–Br/C(sp2)–H functionalization mediated by photoredox and copper cooperative catalysis

For straightforward access to various substituted 1,1-diarylalkanes a photoredox-catalyzed and copper-promoted 1,2-alkylarylation reaction of styrenes has been developed, which uses α-carbonyl alkyl bromides and N,N-disubstituted anilines as functionalization reagents.