Asymmetric Arylation of Diazoesters with Anisoles Enabled by Cooperative Gold and Phosphoric Acid Catalysis

Enantioselective N-H Bond Insertion Reaction of Anilines Enabled by Ruthenium and Chiral Phosphoric Acid Cooperative Catalysis

The enantioselective carbene insertion into N-H bonds of anilines has been realized by cooperative catalysis of ruthenium complexes and chiral phosphoric acids, providing the expected α-aryl glycines in moderate to good yields with high enantioselectivity. Typically, by slightly modifying the reaction conditions, this approach allows the N-H bond insertion reaction to be effective for both α-aryl and α-alkyl diazoacetates for the first time with high enantioselectivity (up to 96% and 95% ee, respectively).

Enantioselective merged gold/organocatalysis

Gold complexes, because of their unique carbophilic nature, have evolved as efficient catalysts for catalyzing various functionalization reactions of C-C multiple bonds. However, the realization of enantioselective transformations via gold catalysis remains challenging due to the geometrical constraints and coordination behaviors of gold complexes. In this context, merged gold/organocatalysis has emerged as one of the intriguing strategies to achieve enantioselective transformations which could not be possible by using a single catalytic system. Historically, in 2009, this field started with the merging of gold with axially chiral Brønsted acids and chiral amines to achieve enantioselective transformations. Since then, based on the unique reactivity profiles offered by each catalyst, several reports utilizing gold in conjunction with various chiral organocatalysts such as amines, Brønsted acids, N-heterocyclic carbenes, hydrogen-bonding and phosphine catalysts have been documented in the literature. This article demonstrates an up-to-date development in this field, especially focusing on the mechanistic interplay of gold catalysts with chiral organocatalysts.

Asymmetric N-Alkylation of 1H-Indoles via Carbene Insertion Reaction

An intermolecular enantioselective N-alkylation reaction of 1H-indoles has been developed by cooperative rhodium and chiral phosphoric acid catalyzed N-H bond insertion reaction. N-Alkyl indoles with newly formed stereocenter adjacent to the indole nitrogen atom are produced in good yields (up to 95 %) with excellent enantioselectivities (up to >99 % ee). Importantly, both α-aryl and α-alkyl diazoacetates are tolerated, which is extremely rare in asymmetric X-H (X=N, O, S et al.) and C-H insertion reactions. With this method, only 0.1 mol % of rhodium catalyst and 2.5 mol % of chiral phosphoric acid are required to complete the conversion as well as achieve the high enantioselectivity. Computational studies reveal the cooperative relay of rhodium and chiral phosphoric acid, and the origin of the chemo and stereoselectivity.

Atroposelective Synthesis of N-N Axially Chiral Bipyrroles via Rhodium-Catalyzed C-H Insertion Reaction

An atroposelective synthesis of bipyrroles with an axially chiral N-N bond has been established via a rhodium-catalyzed C-H bond insertion reaction to provide the desired atropisomers in good yields (up to 97% yield) with good to excellent enantioselectivities (up to 99% ee).

Enantioselective synthesis of α,α-diarylketones by sequential visible light photoactivation and phosphoric acid catalysis

Chiral ketones and their derivatives are useful synthetic intermediates for the synthesis of biologically active natural products and medicinally relevant molecules. Nevertheless, general and broadly applicable methods for enantioenriched acyclic α,α-disubstituted ketones, especially α,α-diarylketones, remain largely underdeveloped, owing to the easy racemization. Here, we report a visible light photoactivation and phosphoric acid-catalyzed alkyne-carbonyl metathesis/transfer hydrogenation one-pot reaction using arylalkyne, benzoquinone, and Hantzsch ester for the expeditious synthesis of α,α-diarylketones with excellent yields and enantioselectivities. In the reaction, three chemical bonds, including C═O, C─C, and C─H, are formed, providing a de novo synthesis reaction for chiral α,α-diarylketones. Moreover, this protocol provides a convenient and practical method to synthesize or modify complex bioactive molecules, including efficient routes to florylpicoxamid and BRL-15572 analogs. Computational mechanistic studies revealed that C-H/π interactions, π-π interaction, and the substituents of Hantzsch ester all play crucial roles in the stereocontrol of the reaction.

Forming All-Carbon Quaternary Centers by Geminal Difunctionalization of Diazo Compounds with N,N-Disubstituted Anilines and Allylic Carbonates

A novel three-component reaction of N,N-disubstituted anilines, diazo compounds, and allylic carbonates has been developed by using a rhodium-palladium dual catalysis, providing an effective protocol for the construction of tetrasubstituted esters bearing an all-carbon quaternary center as well as an allylic moiety in one pot.

Efficient Synthesis of Diaryl Quaternary Centers by Rh(II)/Xantphos Catalyzed Relay C-H Functionalization and Allylic Alkylation

A three-component reaction of N, N-disubstituted aniline, α-diazo ester, and an allylic electrophile has been realized by [Rh(II)]₂ /Xantphos catalysis, providing a direct access to various aniline derivatives bearing diaryl allylic quaternary centers in good yields. The synthetic utility of this protocol was demonstrated by facile derivatization of the products for preparation of biologically relevant molecules and structural scaffolds, which offers a high potential for increasing the molecular diversity. Mechanistic studies identified α, α-diarylacetate species as an active intermediate, thereby revealing the presence of a C(sp² )-H functionalization of aniline derivatives/allylic alkylation cascade in this attractive catalytic transformation.

Multicomponent Assembly of Complex Oxindoles by Enantioselective Cooperative Catalysis

Chiral oxindoles are important chemical scaffolds found in many natural products, and their enantioselective synthesis thus attracts considerable attention. Highly diastereo- and enantioselective synthetic methods for constructing C3 quaternary oxindoles have been well-developed. However, the efficient synthesis of chiral 3-substituted tertiary oxindoles has been rarely reported due to the ease of racemization of the tertiary stereocenter via enolization. Therefore, we herein report on the multicomponent assembly (from N-aryl diazoamides, aldehydes, and enamines/indoles) of complex oxindoles by enantioselective cooperative catalysis. These reactions proceed under mild conditions and show broad substrate scope, affording the desired coupling products (>90 examples) with good to excellent stereocontrol. Additionally, this research also demonstrates the synthetic potential of this annulation by constructing the 6,6,5-tricyclic lactone core structure of Speradine A.

Atroposelective Synthesis of Axially Chiral C2-Arylindoles via Rhodium-Catalyzed Asymmetric C-H Bond Insertion

A highly efficient rhodium-catalyzed formal C-H insertion reaction between indoles and 1-diazonaphthoquinones has been established, providing a novel protocol for the atroposelective synthesis of axially chiral C2-arylindoles (up to 99:1 er) under mild reaction conditions. Typically, only 1 mol % of Rh₂(S-PTTL)₄ is used and the chelation group is not needed for this conversion.