Pd/Xu-Phos-catalyzed asymmetric elimination of fully substituted enol triflates into axially chiral trisubstituted allenes

Enantioselective Arylation of Sulfenamides to Access Sulfilimines Enabled by Palladium Catalysis

Sulfur-containing functional groups have garnered considerable attention due to their common occurrence in ligands, pharmaceuticals, and insecticides. Nevertheless, enantioselective synthesis of sulfilimines, particularly diaryl sulfilimines remains a challenging and persistent goal. Herein we report a highly enantio- and chemoselective cross-coupling of sulfenamides with aryl diazonium salt to construct diverse S(IV) stereocenters by Pd catalysis. Bisphosphine ligands bearing sulfinamide groups play a crucial role in achieving high reactivity and selectivity. This approach provides a general, modular and divergent framework for quickly synthesizing chiral sulfilimines and sulfoximines that are otherwise challenging to access. In addition, the origins of the high chemoselectivity and enantioselectivity were extensively investigated using density functional theory calculations.

Enantioselective Aminosilylation of Alkenes by Palladium/Ming-Phos-Catalyzed Tandem Narasaka-Heck/Silylation Reaction

A Pd-catalyzed enantioselective aminosilylation of alkenes via tandem Aza-Heck/silylation reaction under Pd/Sadphos catalysis is disclosed. A wide array of oxime esters and silicon reagents are tolerated, furnishing the chiral pyrrolines bearing one quaternary or two contiguous stereocenters in good yield with high enantioselectivity. Not only terminal alkenes but also tri-substituented internal alkenes successfully participate in the reaction, delivering vicinal stereocenters in complete diastereoselectivity and high enantioselectivity. DFT study is conducted to probe the reaction pathway and the origin of the enantioselectivity, which revealed that the stereoinduction arises from the weak interaction between the aromatic ring of the substrate fragment and naphthyl group in the ligand.

Catalytic Asymmetric Synthesis of Sulfinamides via Cu-Catalyzed Asymmetric Addition of Aryl Boroxines to Sulfinylamines

The application of sulfinamides has been witnessed in medicinal and agrochemistry with employment in asymmetric transformations. However, methods for their asymmetric catalytic synthesis have rarely been explored. Herein, the catalytic enantioselective addition of aryl boroxines to sulfinylamines via Cu catalyst and the newly developed Xuphos ligand were reported. A series of chiral aryl sulfinamides can be readily accessed in one step. This protocol enables the stereospecific transformation of sulfinamides to sulfonimidoyl fluorides, sulfonimidamides, and sulfonimidate esters. DFT calculations have revealed the reaction pathway, and the migratory insertion is the enantio-determining step. The noncovalent interaction between the oxygen atom of sulfinylamines and the C-H bonds in the ligand is crucial for enantioselectivity control.

Pd-Catalyzed Asymmetric Larock Indole Synthesis to Access Axially Chiral N-Arylindoles

Larock indole synthesis is one of the most straightforward and efficient methods for the synthesis of indoles; however, there has been no asymmetric version yet for the construction of indole-based axially chiral N-arylindoles since its initial report in 1991. Herein we report the first example of an asymmetric Larock indole synthesis by employing a chiral sulfinamide phosphine (SadPhos) ligand (Ming-Phos) with palladium. It allows rapid construction of a wide range of axially chiral N-arylindole compounds in good yields up to 98:2 er. The application of this unique chiral scaffold as an organocatalyst is promising. Furthermore, a kinetic study has revealed that the alkyne migratory insertion is the rate-determining step, which has been proven by the density functional theory (DFT) calculations. Additionally, DFT studies also suggest that the N-C dihedral difference caused by the steric hindrance of the ligand contributes to enantioselectivity control.

Sadphos as Adaptive Ligands in Asymmetric Palladium Catalysis

ConspectusPalladium catalysis, as one of the most important strategies in asymmetric synthesis, has continuously attracted the attention of organic chemists. With the development of chiral ligands, increasingly challenging reactions and substantial progress in asymmetric catalysis are being realized.Since 2014, we have focused on exploiting a series of sulfinamide phosphine ligands called "Sadphos," including Ming-Phos, Xu-Phos, Xiao-Phos, Xiang-Phos, TY-Phos, PC-Phos, GF-Phos, and WJ-Phos. These ligands can be easily prepared in two to four steps using commercial materials. These new types of ligands have shown remarkable performance in transition-metal-catalyzed reactions, especially in Pd-catalyzed transformations. X-ray diffraction analysis, mechanistic studies, and density functional theory calculations have revealed that Sadphos ligands can coordinate with the Pd0 and PdII species in the Pd0/P, Pd0/P,S, or PdII/P,O modes.This Account summarizes our recent efforts toward palladium-catalyzed enantioselective reactions using Sadphos ligands. These ligands were found to be privileged and very crucial to promote the reactions by increasing the reactivity and enantioselectivity. Ming-Phos is an effective ligand in Pd-catalyzed asymmetric coupling and intramolecular Heck reactions, providing highly enantioselective trisubstituted allenes, axially chiral anilides, gem-diarylmethine silanes, and disubstituted dihydroisoquinolinones. Incorporation of an electron-rich cyclohexyl group in the phosphine moiety afforded Xu-Phos, which showed a unique effect in a series of asymmetric transformations, including reductive Heck, dearomative Mizoroki-Heck, tandem Heck/Suzuki coupling, carboiodination, carboamination, and cross-coupling reactions. Using a similar strategy, our group synthesized more electron-rich TY-Phos and Xiang-Phos ligands bearing t-butyl and 1-adamantyl group at P atoms, respectively. Regarding stereoelectronic features, these two characteristic ligands were the best choice to satisfy the requirements of the palladium-catalyzed fluoroarylation of gem-difluoroalkenes, intermolecular α-arylation of aldehydes, carboetherification of alkenyl oximes, and carboheterofunctionalization of 2,3-dihydrofurans. Compared with the aforementioned Sadphos ligands, the attractive features of Xiao-Phos, including high nucleophilicity originating from the CH2PPh2 group and the ortho-substituent effect at the side of the aryl ring, are presumably responsible for its efficiency. The Pd/Xiao-Phos catalyst system shows good performance in a series of cross-coupling reactions of secondary phosphine oxides, affording P-stereogenic products bearing multiple types of molecular skeletons. The modification of the basic Sadphos backbone by introducing a xanthene skeleton motivated us to design and synthesize monophosphines, named PC-Phos and GF-Phos. PC-Phos is effective in various reactions, including arylation of sulfenate anions, denitrogenative cyclization of benzotriazoles, and dearomatization of indoles. The practicability of GF-Phos was validated in the Pd-catalyzed asymmetric three-component coupling of N-tosylhydrazones, aryl halides, and terminal alkynes, as well as in the cross-coupling of N-tosylhydrazones and vinyl iodides with pendent amines. In addition, ferrocene-derived WJ-Phos was employed in the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction, affording axially chiral biaryl monophosphine oxides in excellent enantiomeric excesses.

Ni-catalysed assembly of axially chiral alkenes from alkynyl tetracoordinate borons via 1,3-metallate shift

Asymmetric synthesis based on a metallate shift of tetracoordinate borons is an intriguing and challenging topic. Despite the construction of central chirality from tetracoordinate boron species via a 1,2-metallate shift, catalytic asymmetric synthesis of axially chiral compounds from such boron 'ate' complexes is an ongoing challenge. Axially chiral alkenes have received great attention due to their unique characteristics and intriguing molecular scaffolds. Here we report an enantioselective nickel-catalysed strategy for the construction of axially chiral alkenes via a 1,3-metallate shift of alkynyl tetracoordinate boron species. The chemoselectivity, regioselectivity and atroposelectivity can be regulated and well-controlled from readily accessible starting materials with a cheap transition-metal catalyst. Downstream transformations indicate the powerful conversion ability of such compounds in this protocol, and late-stage elaborations of bioactive compounds can also be achieved. Mechanistic experiments reveal that regioselective syn-addition of an aryl-Ni complex with a carbon-carbon triple bond and subsequent 1,3-phenyl migration are the two key steps for the synthesis of axially chiral alkenes.