Enantio- and Diastereodivergent N-Heterocyclic Carbene/Nickel Dual-Catalyzed Umpolung Propargylic Substitutions of Enals

Enantioselective Cascade Annulation of 1,2,3-Triazoles and Enals Enabled by Sequential Rhodium and Oxidative NHC Catalysis Involving Cleavage, Migration, and Cyclization

The in situ-generated pyrrolin-3-ones serve as novel and versatile synthons, being employed as intermediates for the efficient production of pyrrole-fused lactones with high yield and excellent enantioselectivity. Herein, we introduce emerging rhodium and oxidative N-heterocyclic carbene relay catalysis that enables a highly enantioselective cascade annulation between easily available 1,2,3-triazoles and enals. In this proof-of-concept study, the in situ-generated pyrrolin-3-ones engage α,β-unsaturated acylazolium intermediates generated from enals via oxidative N-heterocyclic carbene catalysis.

Synergistic Cu(II)/Amine-Catalyzed Cyclization of Enynone: Assembly of Tetralone and Tetrahydronaphthylimine

An unprecedented synergistic copper- and amine-catalyzed cyclization of enynone is reported. This reaction features an efficient and straightforward construction of multisubstituted tetralone through an amine-assisted regioselective oxygen atom transfer process and stereoselective intramolecular Michael addition cyclization. Under dehydrative reaction conditions, the synthesis of tetrahydronaphthylimine derivatives with ketone group tolerance is achieved, which could be challenging via traditional methods. The utility of this reaction is demonstrated by further transformations of obtained molecules toward a variety of valuable multisubstituted naphthyl skeletons.

Remote Enantioselective ϵ-Alkylation of Copper Ethynylallenylidenes: Precise Control of Central and Axial Chirality

Chiral tetrasubstituted allenes have emerged as important architectures for engineering biologically active compounds. The construction of unique tetrasubstituted allene scaffolds with precise control of continuous central and axial chirality remains yet to be developed. Here, we report a remote enantioselective ϵ-alkylation of yne-propargylic acetates with enals enabled by NHC and copper cooperative catalysis, leading to a series of tetrasubstituted allenes with excellent enantioselectivities (up to >99 % ee) and diastereoselectivities (up to >95 : 5 dr). This method features high regioselectivity and simultaneous control of axial and central chirality. Mechanistic studies suggest a cooperative activation mode and synergistic control of distal chirality created from the copper ethynylallenylidenes.

Regioselective Alkylacylation of 1,3-Dienes by Merging N-Heterocyclic Carbene Catalysis with Photoinduced Palladium Catalysis

Herein, we develop a dual catalytic platform for the 1,2- or 1,4-alkylacylation reaction of 1,3-dienes with readily available alkyl halides and aldehydes by merging N-heterocyclic carbene catalysis with photoinduced palladium catalysis. A series of β,γ-unsaturated ketones are obtained in good to high yields. Mechanistic studies suggest that this reaction involves a radical process. The direct synthesis of flavanone from salicylaldehyde exemplified the potential capability of this dual catalytic platform.

Nickel-Catalyzed Asymmetric (3 + 2) Annulations of Propargylic Carbonates and Vinylogous Donors via an Alkenylation Pathway

The transition-metal-catalyzed alkenylation strategy of propargylic alcohol derivatives provides an efficient protocol to access multifunctional products in a double-nucleophilic attack pattern. While limited relevant asymmetric examples have been reported via palladium catalysis, here we first demonstrate that a nonprecious Ni(0)-based chiral complex can efficiently promote the tandem substitution process between propargylic carbonates and N-trifluoroethyl ketimines via consecutive aza-vinylogous activations, finally accomplishing a (3 + 2) annulation reaction to afford products embedding a 4-methylene-3,4-dihydro-2H-pyrrole framework with high regio-, diastereo-, and enantiocontrol. Their assemblies with a few all-carbon-based vinylogous precursors are also successful, and enantioenriched adducts containing a 3-methylenecyclopentene scaffold are furnished effectively. The substitution patterns for both types of substrates are substantial, and an array of synthetic elaborations is conducted to deliver more versatile architectures with high application potential. In addition, density functional theory calculations and control experiments have been conducted to rationalize the catalytic pathways and regio- and enantioselectivity control.

Ni/Cu Dual-Catalyzed Propargylation for the Stereodivergent Synthesis of Methohexital

The development of efficient methodologies for the controlled manufacture of specific stereoisomers bearing quaternary stereocenters has prompted advances in a variety of scientific disciplines including pharmaceutical chemistry, materials science, and chemical biology. However, complete control of the absolute and relative stereochemical configurations of alkyne derivatives remains an unmet synthetic challenge. Herein, a Ni/Cu dual-catalyzed asymmetric propargylic substitution reaction is presented to produce propargylated products with all-carbon quaternary stereocenters in high yields with significant diastereo- and enantioselectivities (up to >20:1 dr, >99% ee). The synthesis of all stereochemical variants of methohexital, a widely used sedative-hypnotic drug, exemplifies the efficacy of dual-catalyzed stereodivergent propargylation.

Synergistic Palladium/Copper-Catalyzed 1,4-Difunctionalization of 1,3-Dienes for Stereodivergent Construction of 1,5-Nonadjacent Stereocenters

The construction of two distal stereocenters through a single catalytic process is of great interest in organic synthesis. While there are some successful reports regarding stereodivergent preparation of 1,3- or 1,4-stereocenters, the more challenged 1,5-nonadjacent stereocenters have never been achieved in a stereodivergent fashion. Herein we describe a synergistic palladium/copper catalysis for 1,4-difunctionalization reactions of 1,3-dienes, providing access to 1,5-nonadjacent quaternary stereocenters. Because each of the two catalysts separately controlled one of the newly formed stereocenters, stereodivergent synthesis of all four diastereomers of the products could readily be achieved simply by choosing an appropriate combination of chiral catalysts. Experimental and computational studies supported a mechanism involving a Heck/Tsuji-Trost cascade reaction, and the origins of the stereoselectivity were elucidated.

Enantioselective Construction of Quaternary Stereocenters via Cooperative Photoredox/Fe/Chiral Primary Amine Triple Catalysis

The catalytic and enantioselective construction of quaternary (all-carbon substituents) stereocenters poses a formidable challenge in organic synthesis due to the hindrance caused by steric factors. One conceptually viable and potentially versatile approach is the coupling of a C-C bond through an outer-sphere mechanism, accompanied by the realization of enantiocontrol through cooperative catalysis; however, examples of such processes are yet to be identified. Herein, we present such a method for creating different compounds with quaternary stereocenters by photoredox/Fe/chiral primary amine triple catalysis. This approach facilitates the connection of an unactivated alkyl source with a tertiary alkyl moiety, which is also rare. The scalable process exhibits mild conditions, does not necessitate the use of a base, and possesses a good functional-group tolerance. Preliminary investigations into the underlying mechanisms have provided valuable insights into the reaction pathway.