Activation of “Inert” Alkenyl/Aryl CO Bond and Its Application in Cross-Coupling Reactions

Asymmetric synthesis via stereospecific C-N and C-O bond activation of alkyl amine and alcohol derivatives

This perspective showcases our development of benzylic and allylic amine and alcohol derivatives as electrophiles for stereospecific, nickel-catalyzed cross-coupling reactions, as well as the prior art that inspired our efforts. The success of our effort has relied on the use of benzyl ammonium triflates as electrophiles for cross-couplings via C-N bond activation and benzylic and allylic carboxylates for cross-couplings via C-O bond activation. Our work, along with others' exciting discoveries, has demonstrated the potential of stereospecific, nickel-catalyzed cross-couplings of alkyl electrophiles in asymmetric synthesis, and enables efficient generation of both tertiary and quaternary stereocenters.

Cobalt-Catalyzed Secondary Alkylation of Arenes and Olefins with Alkyl Ethers through the Cleavage of C(sp2)-H and C(sp3)-O Bonds

A novel cobalt-catalyzed C-H alkylation of arenes and olefins is achieved with (pyridin-2-yl)isopropyl amine as an N, N-bidentate directing group. Different linear, branched, and cyclic alkyl ethers were used as practical secondary alkylating reagents through cleavage of C(sp³)-O bond, providing an efficient approach to the synthesis of verstile o-alkylated arylamides and tetrasubstituted acrylamides. Mechanistic studies indicate that cleavage of the inert C(sp³)-O bond involves a cobalt-promoted radical process and that cleavage of the inert C(sp²)-H bond by a cobalt catalyst is a rate-limiting step.

A mild light-induced cleavage of the S-O bond of aryl sulfonate esters enables efficient sulfonylation of vinylarenes

A new mode of S-O bond activation has been discovered, which constitutes novel reactivity of easily available and bench-stable arylsulfonate phenol esters. This protocol enables access to putative sulfonyl radical intermediates, which enable straightforward access to valuable vinyl sulfones.

Nickel-Catalyzed Csp2-Csp3 Bond Formation via C-F Bond Activation

A nickel-catalyzed cross coupling of aryl fluorides via C-F bond activation has been developed. The alkylation method allows selective replacement of aryl fluorides by alkyl groups and enables the synthesis of diverse and otherwise difficult to access scaffolds in good yields.

Photoinduced Deaminative Borylation of Alkylamines

An operationally simple deaminative borylation reaction of primary alkylamines has been developed. The formation of electron-donor-acceptor complexes between N-alkylpyridinium salts and bis(catecholato)diboron enables photoinduced single-electron transfer and fragmentation to carbon-centered radicals, which are subsequently borylated. The mild conditions allow a diverse range of readily available alkylamines to be efficiently converted into synthetically valuable alkylboronic esters under catalyst-free conditions.

Palladium-Catalyzed N-Arylation of Sulfoximines with Aryl Sulfonates

Palladium-catalyzed C-N bond coupling reaction between NH-sulfoximines and aryl halides (e.g., -Br, -I, and -Cl and pseudohalides -OTf and -ONf) was successfully achieved. Nevertheless, aryl tosylates/mesylates left much to be achieved. In this report, a general N-arylation of sulfoximines with aryl sulfonates is described. Using Pd(OAc)₂/MeO-CM-phos complex, the N-aryl sulfoximine products can be obtained in good-to-excellent yields (up to 99%) with good common functional group compatibility. In addition to arene moieties, alkenyl tosylates are shown to be successful coupling partners.

Convenient Method of Synthesizing Aryloxyalkyl Esters from Phenolic Esters Using Halogenated Alcohols

A facile one-pot synthetic method of building aryloxyalkyl esters was developed using various types of phenolic esters with halogenated alcohols. The ready availability of both starting materials, coupled with the required simple experimental technique, enables the current synthetic method of producing aryloxyalkyl esters in a fast and efficient way. It is noteworthy that acyl transfer was demonstrated in this reaction.

A General Palladium-Phosphine Complex To Explore Aryl Tosylates in the N-Arylation of Amines: Scope and Limitations

The scope and limitations of the monoselective N-arylation of various amines by using aryl and hetaryl tosylates are presented. The air-stable and easily accessible Pd(OAc)₂ /CM-phos {CM-phos=2-[2-(dicyclohexylphosphino)phenyl]-1-methyl-1H-indole}catalyst system was able to deal with a wide range of aryl tosylate substrates as well as amine nucleophiles, including primary and secondary cyclic/acyclic aliphatic amines and anilines. NH-Bearing heterocycles such as indole, carbazole, pyrrole, 10-phenothiazine, and 10-phenoxazine were shown to be feasible coupling partners under this catalytic system. The described reaction conditions tolerate a wide range of functional groups and allow an array of aromatic amines as well as unsymmetrical amine products to be easily accessed from the various phenolic derivatives. Interestingly, this catalyst system even offers the opportunity to perform the reaction in water medium. We also report the intermolecular coupling of optically active α-central chiral amines with aryl tosylates without erosion of the enantiomeric purity.

Nickel-Catalyzed Domino Heck Cyclization/Suzuki Coupling for the Synthesis of 3,3-Disubstituted Oxindoles

The first nickel-catalyzed domino Heck cyclization/Suzuki coupling reaction for the synthesis of 3,3-disubstituted oxindoles bearing quaternary all-carbon centers is reported. A wide range of electrophiles, such as aryl iodides, bromides, triflates, and chlorides, are all compatible with the reaction conditions. Moreover, cheap aryl esters, which undergo catalytic C-O bond cleavage, could also be employed as electrophiles. The approach shows good yields and broad scope, complementing a more practical and sustainable alternative to the conventional palladium-based analogues.

Less hindered ligands give improved catalysts for the nickel catalysed Grignard cross-coupling of aromatic ethers

The challenging reaction of unactivated ortho-substituted aromatic ethers with Grignard reagents has been found to be most effectively catalysed using nickel complexes of less sterically hindered ligands.

Efficient and selective hydrogenation of C–O bonds with a simple sodium formate catalyzed by nickel

A Ni-catalyzed hydrogenation of C–O compounds with sodium formate is developed. Various esters, i.e. aryl, alkenyl, benzyl pivalates, and even the aryl ethers, were efficiently reduced with a loading of nickel catalysts down to 0.5 mol%.

Palladium-catalysed coupling of α-halo vinylphosphonate and α-phosphonovinyl sulfonate with alkylzincs: straightforward and versatile synthesis of α-alkyl vinylphosphonates

Easy and efficient access to α-alkylated vinylphosphonates via Pd-catalysed Negishi coupling!

Nickel-catalyzed cross-coupling of β-carbonyl alkenyl pivalates with arylzinc chlorides

The reaction of β-carbonyl alkenyl pivalates with arylzinc reagents was carried out via nickel-catalyzed C–O bond cleavage, forming 3-aryl-substituted α,β-unsaturated carbonyl compounds in moderate to excellent yields.