Cross-coupling reactions by cooperative Pd/Cu or Ni/Cu catalysis based on the catalytic generation of organocopper nucleophiles

Cooperative Cu/Pd-Catalyzed 1,5-Boroacylation of Cyclopropyl-Substituted Alkylidenecyclopropanes

A Cu/Pd-cocatalyzed 1,5-boroacylation of cyclopropyl-substituted ACPs with B2pin2 and acid chlorides has been developed. Using cyclopropyl-substituted ACPs as the starting material, a broad range of 1,5-boroacylated products with multiple functional groups was prepared in good yields with excellent regio- and stereoselectively. Both aromatic and aliphatic acid chlorides were tolerated in this reaction.

Iterative Dual-Metal and Energy Transfer Catalysis Enables Stereodivergence in Alkyne Difunctionalization: Carboboration as Case Study

Stereochemically defined tetrasubstituted olefins are widespread structural elements of organic molecules and key intermediates in organic synthesis. However, flexible methods enabling stereodivergent access to E and Z isomers of fully substituted alkenes from a common precursor represent a significant challenge and are actively sought after in catalysis, especially those amenable to complex multifunctional molecules. Herein, we demonstrate that iterative dual-metal and energy transfer catalysis constitutes a unique platform for achieving stereodivergence in the difunctionalization of internal alkynes. The utility of this approach is showcased by the stereodivergent synthesis of both stereoisomers of tetrasubstituted β-boryl acrylates from internal alkynoates with excellent stereocontrol via sequential carboboration and photoisomerization. The reluctance of electron-deficient internal alkynes to undergo catalytic carboboration has been overcome through cooperative Cu/Pd-catalysis, whereas an Ir complex was identified as a versatile sensitizer that is able to photoisomerize the resulting sterically crowded alkenes. Mechanistic studies by means of quantum-chemical calculations, quenching experiments, and transient absorption spectroscopy have been applied to unveil the mechanism of both steps.

Cu/Pd-catalyzed arylboration of a 1-silyl-1,3-cyclohexadiene for stereocontrolled and diverse cyclohexane/ene synthesis

The synthesis and Cu/Pd-catalyzed arylboration of 1-silyl-1,3-cyclohexadiene is described. This diene is significant as it allows for synthesis of polyfunctional cyclohexane/enes. To achieve high levels of diastereoselectivity, the use of a pyridylidene Cu-complex was employed. In addition, through the use of a chiral catalyst, an enantioselective reaction was possible. Due to the presence of the silyl and boron substituents, the products can be easily diversified into a range of valuable cyclohexane/ene products.

Copper catalyzed borocarbonylation of benzylidenecyclopropanes through selective proximal C-C bond cleavage: synthesis of γ-boryl-γ,δ-unsaturated carbonyl compounds

A copper catalyzed borocarbonylation of BCPs via proximal C-C bond cleavage for the synthesis of γ-boryl-γ,δ-unsaturated carbonyl compounds has been developed. Using substituted benzylidenecyclopropanes (BCPs) and chloroformates as starting material, a broad range of γ-boryl-γ,δ-unsaturated esters were prepared in moderate to excellent yields with excellent regio- and stereoselectivity. Besides, when aliphatic acid chlorides were used in this reaction, γ-boryl-γ,δ-unsaturated ketones could be produced in excellent yields. When substituted BCPs were used as substrates, the borocarbonylation occurred predominantly at the proximal C-C bond trans to the phenyl group in a regio- and stereoselective manner, which leads to the Z-isomers as the products. This efficient methodology involves the cleavage of a C-C bond and the formation of a C-C bond as well as a C-B bond, and provides a new method for the proximal C-C bond difunctionalization of BCPs.

Copper-catalyzed 1,2-Borylacylation of 1,3-Enynes: synthesis of β-Alkynyl ketones

A copper catalyzed 1,2-borylacylation of 1,3-enynes with B₂pin₂ and acid chlorides has been developed. Using readily available 1,3-enynes, B₂pin₂ and acid chlorides as substrates, a range of highly functionalized α,α-disubstituted β-alkynyl ketones were readily prepared under mild conditions in moderate to good yields. The borylacylated products can be easily derivatized to give several valuable structures. Notably, treatment of the products with NaBO₃·4H₂O provided 1,2-allenyl ketones, which is proposed to proceed via a retro-aldol process of the corresponding homopropargyl alcohols.

Cooperative Pd/Cu Catalysis for Alkene Arylboration: Opportunities for Divergent Reactivity

A preeminent challenge in alkene difunctionalization is the control of regio-, diastereo-, and enantioselectivity. In this Perspective, a Pd/Cu-cooperative catalytic system for alkene arylboration is highlighted that allows for the controlled introduction of substituents. In particular, examples that allowed for divergent reactivity from a single substrate based on the tuning of catalysts and reaction conditions are emphasized.

Ligand-controlled, Pd/CuH-catalyzed reductive cross-coupling of terminal alkenes and N-heteroaryl bromides

The reductive cross-coupling of terminal alkenes and N-heterocyclic bromides has been demonstrated by ligand optimization of Pd and CuH catalysis. The optimized ligands are Briphos, a π-acceptor monodentate phosphorus ligand, for Pd catalysis and DTB-DPPBz, a sterically bulky bidentate phosphorus ligand, for CuH catalysis. These conditions were further applied to the gram-scale production of clathryimine B.

Catalytic Arylboration of Spirocyclic Cyclobutenes: Rapid Access to Highly Substituted Spiro[3.n]alkanes

A method to achieve the synthesis of highly substituted spirocyclic cyclobutanes is disclosed. The reaction involves the catalytic arylboration of cyclobutenes. Depending on the substitution pattern of the cyclobutene, either a Cu/Pd- or a Ni-catalyzed reaction was utilized. In the case of the Cu/Pd catalyzed reactions, the identification of a Cu-complex for arylboration was crucial to observe high selectivity. The synthetic utility of the products is demonstrated, and the mechanistic details are discussed.

Nickel-Catalyzed Dearomative Arylboration of Indoles: Regioselective Synthesis of C2- and C3-Borylated Indolines

Indole dearomatization is an important strategy to access indolines: a motif present in a variety of natural products and biologically active molecules. Herein, a method for transition-metal catalyzed regioselective dearomative arylboration of indoles to generate diverse indolines is presented. The method accomplishes intermolecular dearomatization of simple indoles through a migratory insertion pathway on substrates that lack activating or directing groups on the C2- or C3-positions. Synthetically useful C2- and C3-borylated indolines can be accessed through a simple change in N-protecting group in high regio- and diastereoselectivities (up to >40:1 rr and >40:1 dr) from readily available starting materials. Additionally, the origin of regioselectivity was explored experimentally and computationally to uncover the remarkable interplay between carbonyl orientation of the N-protecting group on indole, electronics of the C2-C3 π-bond, and sterics. The method enabled the first enantioselective synthesis of (-)-azamedicarpin.

Modular Synthesis of a Versatile Double-Allylation Reagent for Complex Diol Synthesis

Double-allylation reagents allow for the construction of highly complex molecules in an expedient fashion. We have developed an efficient, modular, and enantioselective approach towards accessing novel variants of these reagents through Cu/Pd-catalyzed alkenylboration of alkenylboron derivatives. Importantly, we demonstrate novel use of an allylBdan reagent directly in a stereocontrolled allylation without initial deprotection to the boronic ester. These allylation products are employed in a second intermolecular allylation to access complex diol motifs, which has yet to be shown with these types of double-allylation reagents. Overall, the modularity of this approach and the ease in which complex structural motifs can be accessed in a rapid manner signify the importance and utility of this method.

C–C and C–X coupling reactions of unactivated alkyl electrophiles using copper catalysis

Copper catalysts enable cross-coupling reactions of unactivated alkyl electrophiles to generate C–C and C–X bonds.

Ligand-controlled diastereodivergent, enantio- and regioselective copper-catalyzed hydroxyalkylboration of 1,3-dienes with ketones

A copper-catalyzed three-component coupling of 1,3-dienes, bis(pinacolato)diboron, and ketones allows for the chemo-, regio-, diastereo- and enantioselective assembly of densely functionalized tertiary homoallylic alcohols. The relative configuration of the vicinal stereocenters is controlled by the chiral ligand employed. Subsequent transformations illustrate the versatility of these valuable chiral building blocks.

(Hetero)arylboration of alkynes: a strategy for the synthesis of α,α-bis(hetero)arylketones

A method for (hetero)arylboration of alkynes is presented. The reaction allows for the synthesis of densely functionalized tetrasubstituted alkenes with control of regioselectivity and diastereoselectivity. The conversion of the products to the corresponding α,α-bis(hetero)arylketones is also shown.