Ping Tian

Cu-Catalyzed Asymmetric Borylative Cyclization of Cyclohexadienone-Containing 1,6-Enynes

The first Cu-catalyzed asymmetric borylative cyclization of cyclohexadienone-containing 1,6-enynes is achieved through a tandem process: selective β-borylation of propargylic ether and subsequent conjugate addition to cyclohexadienone. The reaction proceeds with excellent regioselectivity and enantioselectivity to afford an optically pure cis-hydrobenzofuran framework bearing alkenylboronate and enone substructures. Furthermore, the resulting bicyclic products could be converted to bridged and tricyclic ring structures. This method extends the realm of Cu-catalyzed asymmetric tandem reactions using bis(pinacolato)diboron (B2pin2).The first Cu-catalyzed asymmetric borylative cyclization of cyclohexadienone-containing 1,6-enynes is achieved through a tandem process: selective beta-borylation of propargylic ether and subsequent conjugate addition to cyclohexadienone. The reaction pro

Tunable Arylative Cyclization of 1,6-Enynes Triggered by Rhodium(III)-Catalyzed C–H Activation

Two tunable arylative cyclizations of cyclohexadienone-containing 1,6-enynes are reported via rhodium(III)-catalyzed C-H activation of O-substituted N-hydroxybenzamides. The use of different O substituents, i.e. O-Piv and O-Me, on the directing group allows the formation of either tetracyclic isoquinolones through an Ⓝ-Michael addition process or hydrobenzofurans through a Ⓒ-Michael addition process. Mechanistic investigations of these two cascade reactions clearly indicated that the C-H bond cleavage process was involved in the turnover-limiting step. Furthermore, the cyclization products could be subjected to various transformations for elaborating the pharmaceutically and synthetically valuable potential. This is the first example of a rhodium(III)-catalyzed arylative cyclization reaction of 1,6-enynes, and the results extend the application realm of Cp*Rh(III)-catalyzed C-H activation cascade reactions.

Asymmetric Synthesis of β-Substituted γ-Lactams via Rhodium/Diene-Catalyzed 1,4-Additions: Application to the Synthesis of (R)-Baclofen and (R)-Rolipram

An efficient rhodium/diene-catalyzed asymmetric addition of arylboronic acids to α,β-unsaturated γ-lactams has been developed. The power of this methodology is further demonstrated by the concise synthesis of (R)-baclofen and (R)-rolipram.

Copper-catalyzed asymmetric hydroboration of α-dehydroamino acid derivatives: facile synthesis of chiral β-hydroxy-α-amino acids.

The Cu-catalyzed asymmetric conjugate hydroboration reaction of β-substituted α-dehydroamino acid derivatives has been established, affording enantioenriched syn- and anti-β-boronate-α-amino acid derivatives with excellent combined yields (83-99%, dr ≈ 1:1) and excellent enantioselectivities (92-98% ee). The hydroboration products were expediently converted into valuable β-hydroxy-α-amino acid derivatives, which were widely used in the preparation of chiral drugs and bioactive molecules.

Rhodium-Catalyzed Asymmetric Arylative Cyclization of meso-1,6-Dienynes Leading to Enantioenriched cis-Hydrobenzofurans†

Chiral cis-hydrobenzofurans represent a uniquemotif existing in numerous natural products, for instance, isoambrox, haterumaimide I, rosenonolactone, incarviditone, and millingtonine A (Scheme 1a). Owing to their diverse biological activities, a great deal of attention has been paid to the development of efficient methods toward their enantioselective syntheses. One of the most straightforward and powerful ways to construct such a framework is the catalytic asymmetric desymmetrization of cyclohexadienones (Scheme 1b). In recent elegant reports, Rovis and co-workers demonstrated the feasibility of using chiral-NHC-catalyzed intramolecular Stetter reactions for the asymmetric desymmetrization of cyclohexadienones to prepare chiral cis-hydrobenzofuranones. Very recently, Sasai and co-workers described the use of bifunctional chiral phosphinothiourea catalysts in a intramolecular Rauhut–Currier reaction for the enantioselective discrimination of cyclohexadienones. Although these protocols proved to be highly effective, their efforts were mainly focused on the application of chiral organocatalysts in intramolecular reactions with a limited substrate scope. Moreover, transition metal catalyzed asymmetric desymmetrization of cyclohexadienones is quite scarce. During our continuous efforts in exploring rhodium/chiral diene-catalyzed asymmetric arylation, we envisioned that a rhodium-catalyzed tandem arylrhodation/conjugate addition reaction of cyclohexadienone-containing 1,6-dienynes, which are accessible from dearomatization of corresponding phenols, would provide a novel approach to these enantioenriched cis-hydrobenzofurans (Scheme 1c). However, two major concerns need to be addressed in this rhodium-catalyzed asymmetric desymmetrization process.

Efficient Access to Bicyclo[4.3.0]nonanes: Copper‐Catalyzed Asymmetric Silylative Cyclization of Cyclohexadienone‐Tethered Allenes

The creation of three consecutive chiral carbon centers in one step is achieved using Cu-catalyzed asymmetric silylative cyclization of cyclohexadienone-tethered allenes. Through regioselective β-silylation of the allene and subsequent enantioselective 1,4-addition to cyclohexadienone, this tandem reaction could afford cis-hydrobenzofuran, cis-hydroindole, and cis-hydroindene frameworks with excellent yields (80-98%) and enantioselectivities (94-98% ee) bearing vinylsilane and enone substructures. Meanwhile, this mild transformation is generally compatible with a wide range of functional groups, which allows further conversion of the bicyclic products to bridged and tricyclic ring structures.

Copper(I)-catalyzed enantioselective hydroboration of cyclopropenes: facile synthesis of optically active cyclopropylboronates

Copper(I)-catalyzed enantioselective hydroboration of 3-aryl substituted cyclopropene-3-carboxylate is described, providing chiral cyclopropylboronates with excellent enantioselectivities (89–95% ee) in moderate to high yields (55–86%). The non-directing effect of the ester group was observed, and the reaction proceeded with solely trans-selectivity. The chiral boronates could be conveniently converted into chiral 1,2-diaryl substituted cyclopropane derivatives.

Bisannulation of Benzamides and Cyclohexadienone-Tethered Allenes Triggered by Cp*Rh(III)-Catalyzed C–H Activation and Relay Ene Reaction

The diastereoselective bisannulation of N-(pivaloyloxy)benzamides and cyclohexadienone-tethered allenes was accomplished through Cp*Rh(III)-catalyzed C-H activation and relay ene reaction, providing a 3-isoquinolonyl cis-hydrobenzofuran framework with high yields and diastereoselectivities. This reaction tolerates a wide range of functional groups, enabling further conversions to tricyclic and bridged-ring structures. Moreover, the dearomatization modification of phenol-contained bioactive molecule is also elaborated.

CuH-Catalyzed Asymmetric Intramolecular Reductive Coupling of Allenes to Enones

The CuH-catalyzed asymmetric intramolecular reductive coupling of allenes to enones is successfully realized, providing cis-hydrobenzofurans with promising yields and excellent enantioselectivities. Such brilliant enantioselectivities are partially contributed by CuH-catalyzed favorable kinetic resolution of the cyclization products. This protocol tolerates a broad range of functional groups, allowing for further construction of tricyclic and bridged-ring structures. Moreover, the meta-chiral functionalization of 4-substituted phenol and asymmetric dearomatization modification of phenol-contained bioactive molecules are also described.

Recent Progress on Cu-Catalyzed Asymmetric Conjugate Borylation toα,β-Unsaturated Compounds

Abstract Organoborons are an important class of organic compounds, because organoboronic acids and their derivatives can be readily converted into a wide variety of functionalities in a stereospecific manner. Cu-catalyzed asymmetric conjugate borylation of unsaturated compounds with bis(pinacolato)diboron (B2pin2) has emerged as a novel synthetic tool to afford a variety of organoboron compounds. Herein, this research progress, which involves using bisphosphine, N-heterocyclic carbine, and other chiral ligands, is summarized.