Enantioselective Copper-Catalyzed [3 + 3] Cycloaddition of Tertiary Propargylic Esters with 1H-Pyrazol-5(4H)-ones toward Optically Active Spirooxindoles

Copper-Catalyzed Enantioselective (3 + 3) Cycloaddition of Ethynyl Methylene Cyclic Carbamates with N,N'-Cyclic Azomethine Imines

A copper-catalyzed asymmetric cross 1,3-dipolar cycloaddition between 2-aminoallyl zwitterions generated in situ from ethynyl methylene cyclic carbamates and N,N'-cyclic azomethine imines has been realized. The reaction, which utilizes a commercially available chiral tridentate N-ligand, delivers a range of functionally rich chiral hexahydro-8H-pyrazolo[1,2-a][1,2,4]triazin-8-one derivatives in 51-99% yields with good to high enantioselectivities (44-95% ee).

Copper-catalyzed enantioselective propargylic [3 + 2] cycloaddition: access to oxygen heterocycles featuring a CF3-substituted quaternary stereocenter

A Cu(I)-Pybox-diPh catalyzed enantioselective [3 + 2] cycloaddition reaction of CF3-substituted tertiary propargylic esters as C2-bis-electrophiles with cyclic 1,3-dicarbonyl compounds as C,O-bis-nucleophiles has been reported. The methodology furnishes a variety of optically active oxygen heterocycles containing a CF3-substituted quaternary stereocenter in good yields and enantioselectivities. Moreover, the scalability of the reaction and transformations of chiral compounds into their derivatives demonstrated the synthetic and practical relevance of the approach.

Enantioselective Synthesis of Spirooxindole-Pyran and Furan Scaffolds via Copper-Catalyzed Formal (3+3) and (3+2) Cycloaddition of Isatin-Derived Propargylic Esters

Herein, we report a copper-catalyzed enantioselective formal (3+3) and (3+2) cycloaddition reaction of isatin-derived tertiary propargylic esters with N,N-dimethylbarbituric acid and 4-hydroxycoumarins, respectively. In this process, the tertiary propargylic ester serves as both C3- and C2-synthons, facilitating the synthesis of optically active spirooxindole-pyran and furan scaffolds featuring an all-carbon quaternary stereocenter. The reaction delivers these spirocyclic frameworks in good yields with high enantioselectivities. Additionally, the scalability of both the reactions and the transformation of chiral intermediates into valuable structures emphasize the synthetic and practical importance of this strategy.

Chiral Phosphoric Acid-Catalyzed Enantioselective Synthesis of 2,2-Disubstituted 2,3-Dihydro-4-quinolones from Isatins and 2'-Aminoacetophenones

Herein, we present the enantioselective synthesis of 2,3-dihydro-4-quinolones bearing chiral tetrasubstituted carbons from isatins and 2'-aminoacetophenones. The transformation is mediated by a chiral phosphoric acid catalyst and proceeds via an in situ generated ketimine and subsequent enantioselective intramolecular cyclization. The methodology features a broad scope and functional group tolerance with yields and enantioselectivities of up to 99% and 98% ee. Detailed density functional theory (DFT) calculations support the proposed reaction mechanism and the origin of asymmetric induction.

Recent Developments in Copper-Catalyzed Annulations for Synthesis of Spirooxindoles

Spirooxindoles represent a special scaffold for pharmaceuticals and natural products, and significant advancements have been achieved in their synthesis in recent years. Among these, transition metal catalysis, particularly copper catalysis, has emerged as an efficient and reliable method for the synthesis of spirooxindoles. Based on different reaction types, two distinct substrate types have been summarized and classified by us for constructing spirooxindole scaffolds via intramolecular and intermolecular annulations. This review outlines the latest advancements in copper-catalyzed cyclization reactions for synthesizing spirooxindoles and provides detailed insights into the types of annulation reactions and their possible reaction mechanisms.

Enantioselective propargylic amination and related tandem sequences to α-tertiary ethynylamines and azacycles

Chiral α-tertiary amines and related azacycles are sought-after compounds for drug development. Despite progress in the catalytic asymmetric construction of aza-quaternary stereocentres, enantioselective synthesis of multifunctional α-tertiary amines remains underdeveloped. Enantioenriched α-disubstituted α-ethynylamines are attractive synthons for constructing chiral α-tertiary amines and azacycles, but methods for their catalytic enantioselective synthesis need to be expanded. Here we describe an enantioselective asymmetric Cu(I)-catalysed propargylic amination (ACPA) of simple ketone-derived propargylic carbonates to give both α-dialkylated and α-alkyl-α-aryl α-tertiary ethynylamines. Sterically confined pyridinebisoxazoline (PYBOX) ligands, with a C4 shielding group and relaying groups, play a key role in achieving excellent enantioselectivity. The syntheses of quaternary 2,5-dihydropyrroles, dihydroquinines, dihydrobenzoquinolines and dihydroquinolino[1,2-α]quinolines are reported, and the synthetic value is further demonstrated by the enantioselective catalytic total synthesis of a selective multi-target β-secretase inhibitor. Enantioselective Cu-catalysed propargylic substitutions with O- and C-centred nucleophiles are also realized, further demonstrating the potential of the PYBOX ligand.

Copper-Catalyzed Enantioselective Formal [4 + 1] and [3 + 3] Cycloaddition of Ethynylethylene Carbonates

Herein we employed ethynylethylene carbonates (EECs) to achieve formal [4 + 1] and [3 + 3] cycloaddition with cyclic 1,3-dicarbonyl compounds. On one hand, EECs with styryl substitution could undergo a remotely controlled enantioselective [4 + 1] cycloaddition reaction. This reaction exhibits good chemoselectivity, regioselectivity, and enantioselectivity. In addition, a [3 + 3] cycloaddition reaction of EECs with cyclic 1,3-dicarbonyl compounds was also achieved, leading to a series of 4H-pyrans with impressive chemoselectivity and enantioselectivity.

Enantioselective synthesis of 3-hydroxy- and 3-amino-3-alkynyl-2-oxindoles by the dimethylzinc-mediated addition of terminal alkynes to isatins and isatin-derived ketimines

A common protocol for enantioselective alkynylation of isatins and isatin-derived ketimines using terminal alkynes and Me2Zn in the presence of a catalytic amount of a chiral perhydro-1,3-benzoxazine with moderate to excellent enantioselectivity under mild reaction conditions is described. The additions to ketimines present a novel approach to chiral amines being derivatives of oxindoles. The reaction is broad in scope with respect to aryl- and alkyl-substituted terminal alkynes and isatin derivatives. In isatins, the alkynylation occurs at the Si face of the carbonyl group, whereas in the ketimine derivatives it occurs at the Re face of the imine.

Stereoselective synthesis of C3-tetrasubstituted oxindoles via copper catalyzed asymmetric propargylation

Herein, a copper catalyzed asymmetric propargylation of 2-oxindole-3-carboxylate esters with terminal propargylic esters is described. This strategy successfully provides a direct approach to constructing a broad range of chiral C3-tetrasubstituted oxindoles with contiguous tertiary and quaternary carbon stereocenters in high yields and excellent enantioselectivities (16 examples, up to 99% yield and 98% ee). Moreover, the diastereoisomers of the two newly formed stereocenters can be separated by silica gel chromatography, thereby providing a valuable stereoselective access to all four possible stereoisomers of C3-tetrasubstituted oxindoles.

Asymmetric Synthesis of Structurally Sophisticated Spirocyclic Pyrano[2,3-c]pyrazole Derivatives Bearing a Chiral Quaternary Carbon Center

A carbene-catalyzed enantio- and diastereoselective [2 + 4] cycloaddition reaction is developed for quick and efficient access to structurally complex multicyclic pyrano[2,3-c]pyrazole molecules. The reaction tolerates a broad scope of substrates bearing various substitution patterns, with the multicyclic pyrano[2,3-c]pyrazole products afforded in generally good to excellent yields and optical purities. The chiral molecules obtained from this approach has found promising applications in the development of novel bacteriacides for plant protection.

Intramolecular Copper-Catalyzed Asymmetric Propargylic [4 + 2]- Cycloaddition toward Optically Active Tetrahydroisoindolo[2,1-a]quinoxalines

An intramolecular Cu-catalyzed asymmetric propargylic [4 + 2] cycloaddition of bis-N-nucleophile-functionalized propargylic esters has been realized in the support of a chiral tridentate N-ligand, (S,S)-Pybox-diOAc, leading to chiral tetrahydroisoindolo[2,1-a]quinoxalines in high yields and with good to excellent enantioselectivities. The reaction features high efficiency, simplicity, and broad substrate scope, thus providing a powerful and concise strategy for stereoselective access to optically active polycyclic heterocycle frameworks that are otherwise difficult to synthesize.

Recent advances in the applications of pyrazolone derivatives in enantioselective synthesis

Pyrazolones and pyrazoles, featuring nitrogen-nitrogen bonds, are two of the most important classes of heterocycles, owing to their widespread occurrence in medicinal chemistry and functional materials. The last decade has witnessed a rapid increase in the construction of chiral pyrazolone and pyrazole derivatives, with the application of pyrazolone derivatives as powerful synthons. Since our last review in 2018, a large number of new achievements has emerged in this area, requiring a timely update. Thus, this review summarizes these elegant achievements based on the multiple reactive sites of different pyrazolone synthons. In addition, important mechanisms and interesting biological investigations relating to the corresponding products are also discussed.

Synthesis of pyranopyrazoles with a chiral quaternary carbon stereocenter via copper-catalyzed enantioselective [3 + 3] cycloaddition

A copper-catalyzed enantioselective [3 + 3] cycloaddition of propargyl carbonates and pyrazolones has been disclosed. This reaction provided an efficient route to synthesize pyranopyrazoles containing a chiral quaternary carbon stereocenter in good yields with good to excellent enantioselectivities. In addition, the hydroxyl group in the products could be conveniently transformed into a variety of functional groups, such as aldehyde, nitrile, alkene, ester and amide groups, which further increased the synthetic value of this reaction.

Stereoselective sulfenylation of oxindole-derived propargyl alcohols to access sulfenylated-3-alkenyloxindoles

A Ca-catalyzed, tetrasubstituted alkenyl-sulfenylation was achieved using readily available aryl/alkyl thiols and easily prepared oxindole-derived propargyl alcohols under solvent-free conditions. The reaction proceeded with hydrogen bonding assisted regioselective α-thiolation and subsequent calcium catalyzed stereoselective alkenylation to yield E-alkenyl thioethers with high diastereoselectivity.

Divergent Reactivity of δ- and β'-Acetoxy Allenoates with 2-Sulfonamidoindoles via Phosphine Catalysis: Entry to Dihydro-α-carboline, α-Carboline, and Spiro-cyclopentene Motifs

The reactivity of 2-sulfonamidoindoles with acetoxy allenoates under phosphine catalysis depends on the disposition of the acetoxy (OAc) group on the allenoate. In the temperature-controlled [3 + 3] annulations, δ-acetoxy allenoates afforded dihydrocarboline and carboline scaffolds with carbon-nitrogen nucleophilic 2-sulfonamidoindoles, in which allenoate serves as a β-, γ-, and δ-carbon donor. At room temperature (25 °C), dihydro-α-carboline motifs were obtained exclusively through Michael addition, 1,4-proton shift, isomerization, 1,2-proton transfer, phosphine elimination, and aza-Michael addition. The higher temperature (80 °C) cascade protocol using Ph₃P-Cs₂CO₃ combination involves addition-elimination, aza-Claisen rearrangement, tosyl migration, and aromatization as key steps to give α-carbolines containing tosyl functionality at the γ-carbon. In contrast, with β'-acetoxy allenoate, 2-sulfonamidoindole acts only as a carbo-nucleophile in (p-tolyl)₃P-directed [4 + 1] spiro-annulation, leading to five-membered spiro-carbocyclic motifs essentially as single diastereomers (dr >20:1) via chemoselective carbo-annulation.