Efficient Catalytic Kinetic Resolution of Spiro‐epoxyoxindoles with Concomitant Asymmetric Friedel–Crafts Alkylation of Indoles

An efficient process involving the catalytic kinetic resolution of racemic spiro‐epoxyoxindoles with the simultaneous enantioselective Friedel–Crafts alkylation of indoles has been realized using a chiral phosphoric acid catalyst. The reaction provides two useful intermediates in high yields and excellent enantioselectivities. Performing the catalysis on a gram scale led to (R)‐3‐(3‐indolyl)‐oxindole‐3‐methanol, which was used in the asymmetric formal total synthesis of (+)‐gliocladin C. Notably, the enantiomers (S)‐3‐(3‐indolyl)‐oxindole‐3‐methanol can be obtained easily by the reaction of the resolved spiro‐epoxyoxindole with indole.     

Asymmetric Synthesis of Spiropyrazolones by Rhodium‐Catalyzed C(sp2)−H Functionalization/Annulation Reactions

Rhodium‐catalyzed C(sp²)−H functionalization reactions of 4‐aryl‐5‐pyrazolones followed by [3+2] annulation reactions with alkynes provide rapid access to highly enantioenriched five‐membered‐ring 4‐spiro‐5‐pyrazolones. The use of a chiral SCpRh catalyst enabled the synthesis of a large range of spiropyrazolones with all‐carbon quaternary stereogenic centers in up to 99 % yield and 98 % ee from readily available substrates.     

Copper‐Catalyzed Enantioselective Alkylation of Enolizable Ketimines with Organomagnesium Reagents

Inexpensive and readily available organomagnesium reagents were used for the catalytic enantioselective alkylation of enolizable N ‐sulfonyl ketimines. The low reactivity and competing enolization of the ketimines was overcome by the use of a copper–phosphine chiral catalyst, which also rendered the transformation highly chemoselective and enantioselective for a broad range of ketimine substrates.     

Organocatalytic Friedel–Crafts Alkylation/Lactonization Reaction of Naphthols with 3‐Trifluoroethylidene Oxindoles: The Asymmetric Synthesis of Dihydrocoumarins

Naphthols and 3‐trifluoroethylidene oxindoles were found to undergo an asymmetric Friedel–Crafts alkylation/lactonization reaction, catalyzed by only 2.5 mol % of a quinine‐derived squaramide catalyst, to afford the corresponding α‐aryl‐β‐trifluoromethyl dihydrocoumarin derivatives in high yields (up to 99 %) with excellent enantio‐ and diastereoselectivities (up to 98 % ee , >20:1 d.r.). Importantly, the lactonization proceeded by nucleophilic attack of the naphthol hydroxy group at the amide motif of the oxindoles under mild reaction conditions. This protocol represents a new strategy for the formation of dihydrocoumarins by an efficient intramolecular amide C−N bond‐cleavage and esterification process.     

Thiourea‐Catalyzed Asymmetric Michael Addition of Carbazolones to 2‐Chloroacrylonitrile: Total Synthesis of 5,22‐Dioxokopsane,Kopsinidine C,and Demethoxycarbonylkopsin

A modified Takemoto catalyst enabled the asymmetric Michael addition of carbazolones to 2‐chloroacrylonitrile to afford 3,3‐disubstituted carbazolones with excellent enantioselectivity. This method was successfully applied to total syntheses of three Kopsia alkaloids which featured an unprecedented Mn^III‐mediated oxidative cyclization to create the caged ring system and a SmI₂‐mediated reductive coupling as key steps.     

Construction of Chiral Tetrahydro‐β‐Carbolines: Asymmetric Pictet–Spengler Reaction of Indolyl Dihydropyridines

A highly efficient synthesis of the enantioenriched tetrahydro‐β‐carbolines was developed by using a chiral phosphoric acid catalyzed Pictet–Spengler reaction of indolyl dihydropyridines. The reaction proceeds under mild reaction conditions to afford the desired chiral tetrahydro‐β‐carbolines in good to excellent yields (up to 96 %) and high enantioselectivities (up to 99 % ee ). With this method, a formal synthesis of tangutorine and a total synthesis of deplancheine were achieved in a highly efficient manner.     

Enantioselective Rhodium‐Catalyzed Addition of Arylboroxines to N‐Unprotected Ketimines: Efficient Synthesis of Cipargamin

Highly enantioselective rhodium‐catalyzed addition of arylboroxines to N‐unprotected ketimines is realized for the first time by employing chiral BIBOP‐type ligands with a Rh loading as low as 1 mol %. A range of chiral α‐trifluoromethyl‐α,α‐diaryl α‐tertiary amines or 3‐amino‐3‐aryloxindoles were formed with excellent ee values and yields by employing either WingPhos or PFBO‐BIBOP as the ligand. The method has enabled an efficient enantioselective synthesis of cipargamin.