Copper-Catalyzed Asymmetric Nucleophilic Opening of 1,1,2,2-Tetrasubstituted Donor-Acceptor Cyclopropanes for the Synthesis of α-Tertiary Amines

Catalytic asymmetric transformation of donor-acceptor cyclopropanes (DACs) has been proven to be a highly valuable and robust strategy to construct diverse types of enantioenriched molecules. However, the use of 1,1,2,2-tetrasubstituted DACs to form products bearing quaternary stereocenters remains a long-term unsolved challenge. Here, we report the copper-catalyzed asymmetric aminative ring opening of tetrasubstituted alkynyl DACs that delivers a myriad of α-tertiary amines with high levels of enantioselectivities. The alkyne, amine, and ester moieties within the products enable diverse further applications, including the asymmetric synthesis of bioactive molecules. Mechanistic studies indicate that the zwitterionic intermediate bearing a copper-acetylide unit plays a key role in the process, which represents a new mode for achieving catalytic asymmetric transformation of DACs.

Copper-Catalyzed Dearomative [3 + 2] Annulation of Indoles with 2-Iodoacetic Acid

An efficient copper-catalyzed dearomative [3 + 2] annulation of indoles with 2-iodoacetic acid is developed. By employing Cu(OTf)2/2,2'-bis(2-oxazoline) as the catalyst and LPO as the oxidant, a series of indoline-fused butyrolactones were synthesized in moderate to good yields. The reaction features mild conditions, a broad substrate scope, and readily available starting materials. Furthermore, synthetic transformations of the products were conducted to demonstrate the practical utility of this reaction.

Tandem Dearomative/Rearomative (3 + 2) Annulation of Aroyl-Substituted Donor-Acceptor Cyclopropanes with Benzothiazoles

A series of benzo[d]pyrrolo[2,1-b]thiazoles was synthesized by (3 + 2) annulation of aroyl-substituted donor-acceptor cyclopropanes with benzothiazoles. The annulation, promoted by a substoichiometric amount of Sc(OTf)₃, takes place through the formation of the respective dearomatized (3 + 2) adducts, followed by unexpected decarbethoxylative and dehydrogenative rearomatization to afford fully aromatized products. The unusual reactivity is attributed to the presence of an extra aroyl group in the donor-acceptor cyclopropanes.

Computational insight into the mechanism and stereoselectivity of cycloaddition between donor-acceptor spirocyclopropane and aldehyde catalyzed by Brønsted acid TsOH

The mechanism and diastereoselectivity of the cycloaddition reaction between D-A spirocyclopropane and aldehydes, catalyzed by para-toluenesulfonic acid (TsOH) in dichloromethane to produce 2,5-disubstituted tetrahydrofuran-type lignans, have been investigated by density functional theory (DFT) at the M06-2X/6-311+G(d,p)//B3LYP-D3/6-31G(d,p) level combined with the solvation SMD model. Our calculations show that the entire reaction process includes three stages: the activation of the D-A cyclopropane by Brønsted acid, TsOH, the nucleophilic attack of the aldehyde on the spirocyclopropane, and the formation of the final product, 2,5-disubstituted tetrahydrofuran. It was concluded from the conceptual density functional theory (CDFT) reactivity index analysis that aldehydes with electron-rich substituents are more nucleophilic and more favorable for the reaction to proceed. Furthermore, based on the analyses of energetics as well as the noncovalent interaction (NCI) and reduced density gradient (RDG) in the key transition states, the origin of stereoselectivity was revealed to be determined thermodynamically rather than kinetically. The present work explains the experimental phenomenon well, and provides useful theoretical information for the future design of similar reactions.

Facilitating Rh-Catalyzed C-H Alkylation of (Hetero)arenes and 6-Arylpurine Nucleosides (Nucleotides) with Electrochemistry

An electrochemical approach to promote the ortho-C-H alkylation of (hetero)arenes via rhodium catalysis under mild conditions is described. This approach features mild conditions with high levels of regio- and monoselectivity that tolerate a variety of aromatic and heteroaromatic groups and offers a widely applicable method for late-stage diversification of complex molecular architectures including tryptophan, estrone, diazepam, nucleosides, and nucleotides. Alkyl boronic acids and esters and alkyl trifluoroborates are demonstrated as suitable coupling partners. The isolation of key rhodium intermediates and mechanistic studies provided strong support for a rhodium(III/IV or V) regime.

Copper-Catalyzed Conjugate Additions to Isocyanoalkenes

A copper iodide-Pyox complex catalyzes the first conjugate addition of diverse sulfur, nitrogen, and carbon nucleophiles to isocyanoalkenes. The anionic addition generates metalated isocyanoalkanes capable of S_Ni displacements, providing a rapid route to a series of functionalized, cyclic isocyanoalkanes. The Cu(I)I-Pyox complex efficiently catalyzes a first-in-class conjugate addition affording a range of complex, functionalized isocyanoalkanes that are otherwise challenging to synthesize while laying a foundation for catalytic reactions that maintain the isocyanide group.

Asymmetric Domino Heck/Dearomatization Reaction of β-Naphthols to Construct Indole-Terpenoid Frameworks

A palladium-catalyzed enantioselective Heck cyclization/dearomatization cascade via capturing the cyclized Heck π-allylpalladium intermediate by β-naphthols is reported, which provides a new strategy for the construction of chiral indole-terpenoid frameworks. This method affords indole-functionalized β-naphthalenone compounds bearing an all-carbon-substituted quaternary chiral center in excellent yields (up to 92%) and enantioselectivities (up to 94% ee). In addition, the utility of this method is showcased by the gram-scale syntheses and diverse transformations of the dearomatized products.

Catalytic (3 + 2) annulation of donor-acceptor aminocyclopropane monoesters and indoles

The efficient catalytic activation of donor-acceptor aminocyclopropanes lacking the commonly used diester acceptor is reported here in a (3 + 2) dearomative annulation with indoles. Bench-stable tosyl-protected aminocyclopropyl esters were converted into cycloadducts in 46-95% yields and up to 95 : 5 diastereomeric ratio using catalytic amounts of triethylsilyl triflimide. Tricyclic indoline frameworks containing four stereogenic centers including all-carbon quaternary centers were obtained.

Is Cu(iii) a necessary intermediate in Cu-mediated coupling reactions? A mechanistic point of view

The different pathways have been summarized to disclose the key intermediate in copper-mediated coupling reactions.

“In situ immobilization” of a multicomponent chiral catalyst (MCC) via non-covalent interactions for heterogeneous asymmetric hydrogenation reactions

Novel hybrid catalysts that resulted from the anchoring of pyrene-tagged Rh(i) complexes onto graphene materials via π–π stacking interactions show excellent catalytic activity towards the hydrogenation of dehydroamino acid.

Lewis acid catalysed asymmetric cascade reaction of cyclopropyl ketones: concise synthesis of pyrrolobenzothiazoles

A concise method to synthesize pyrrolobenzothiazoles via a cascade reaction of cyclopropyl ketones was developed by using a chiral N,N′-dioxide-scandium(iii) complex catalyst.

Enantioselective Synthesis of Fused Polycyclic Tropanes via Dearomative [3 + 2] Cycloaddition Reactions of 2-Nitrobenzofurans

A straight synthetic approach to fused polycyclic tropane scaffold formation through an asymmetric dearomatization cycloaddition process of 2-nitrobenzofurans with cyclic azomethine ylides was successfully developed. In the presence of a chiral copper complex, derived from Cu(OAc)₂ and a diphosphine ligand, a series of fused polycyclic tropane derivatives were obtained in high yields (75-91%) with excellent enantioselectivities (90-98%). The utility of this method was showcased by the facile transformation of product.

Enantioselective dearomative [3+2] cycloaddition of 2-nitrobenzofurans with aldehyde-derived Morita–Baylis–Hillman carbonates

The phosphine-catalyzed asymmetric dearomative [3+2] cycloaddition of 2-nitrobenzofurans with aldehyde-derived MBH carbonates or allenoates was developed.