This work describes the cross-electrophile methylation of aryl bromides and aryl tosylates with methyl tosylate. The mild reaction conditions allow effective methylation of a wide set of heteroaryl electrophiles and dimethylation of dibromoarenes.

AbstractThe construction of all C(sp3) quaternary centers has been successfully achieved under Ni-catalyzed cross-electrophile coupling of allylic carbonates with unactivated tertiary alkyl halides. For allylic carbonates bearing C1 or C3 substituents, the reaction affords excellent regioselectivity through the addition of alkyl groups to the unsubstituted allylic carbon terminus. The allylic alkylation method also exhibits excellent functional-group compatibility, and delivers the products with high E selectivity.

AbstractThe construction of all C(sp3) quaternary centers has been successfully achieved under Ni-catalyzed cross-electrophile coupling of allylic carbonates with unactivated tertiary alkyl halides. For allylic carbonates bearing C1 or C3 substituents, the reaction affords excellent regioselectivity through the addition of alkyl groups to the unsubstituted allylic carbon terminus. The allylic alkylation method also exhibits excellent functional-group compatibility, and delivers the products with high E selectivity.

The synthesis of alkyl esters from readily available alkyl halides and chloroformates was achieved for the first time using a mild Ni-catalyzed reductive coupling protocol. Unactivated primary and secondary alkyl iodides as well as glycosyl, benzyl, and aminomethyl halides were successfully employed to yield products in moderate to excellent yields with high functional group tolerance.

A mild Ni-catalyzed reductive arylation of tertiary alkyl halides with aryl bromides has been developed that delivers products bearing all-carbon quaternary centers in moderate to excellent yields with excellent functional group tolerance. Electron-deficient arenes are generally more effective in inhibiting alkyl isomerization. The reactions proceed successfully with pyridine or 4-(dimethylamino)pyridine, while imidazolium salts slightly enhance the coupling efficiency.

The present work disclosed a considerably improved method for the construction of alkyl–aryl ketones by the direct coupling of unactivated alkyl bromides with 1.5 equiv. of acids. In addition, the synthesis of aroyl C-glycosides was first achieved by the reductive coupling of 1-glycosyl bromides with acid derivatives, which may otherwise require multi-step synthesis.

This paper highlights Ni-catalyzed reductive trapping of secondary and tertiary alkyl radicals with both electron-rich and electron-deficient aryl isocyanides using zinc as the terminal reductant, affording 6-alkylated phenanthridine in good yields. The employment of carbene ligands necessitates the alkyl radical process, and represents the first utility in the Ni-catalyzed reductive conditions for the generation of unactivated alkyl radicals from the halide precursors.

Reported herein are the solid state studies of guanidinium/carboxylate salts or the zwitterionic species derived from amino acids. It was disclosed that carboxylates tend to bond to the two unsubstituted external guanidine (N–H)s, adopting assembly modes A and C depending on the geometry of the linkers. Rigid linkers that inhibit the guanidine and carboxylate planes parallel or on the same plane tend to give helical tapes. Bonding of carboxylate to the internal (N–H)s was observed (mode D) only when the external (N–H)s are not available as in 5, suggesting that external bonding modes A and C are possibly energetically more favored than the internal modes B and D. This work may be useful for the development of complex linear particularly helical structures and dimeric structures in polar solvents.Reported herein are the solid state studies of guanidinium/carboxylate salts or the zwitterionic species derived from amino acids. It was disclosed that carboxylates tend to bond to the two unsubstituted external guanidine (N–H)s, adopting assembly modes A and C depending on the geometry of the linkers. Bonding of carboxylate to the internal (N–H)s was observed only when the external (N–H)s are not available as in 5. This work may be useful for the development of complex linear particularly helical structures and dimeric structures in polar solvents.

This work highlights Ni-catalyzed reductive coupling of alkyl acids with alkyl halides, particularly sterically hindered unactivated tertiary alkyl bromides for the production of all carbon quaternary ketones. The reductive strategy is applicable to α-selective synthesis of saturated, fully oxygenated C-acyl glycosides through easy manipulations of the readily available sugar bromides and alkyl acids, avoiding otherwise difficult multistep conversions. Initial mechanistic studies suggest that a radical chain mechanism (cycle B, Scheme 1) may be plausible, wherein MgCl2 promotes the reduction of NiII complexes.

Methylation of unactivated alkyl halides and acid chlorides under Ni-catalyzed reductive coupling conditions led to efficient formation of methylated alkanes and ketones using methyl p-methyl tosylate as the methylation reagent. Moderate to excellent coupling yields as well as excellent functional group tolerance were observed under the present mild and easy-to-operate reaction conditions.

The reductive coupling protocol to intramolecular cyclization of dihaloalkanes is presented. It leads to five- and six-membered rings, with the former being more efficient. The incorporation of secondary alkyl halides generally promotes coupling efficiency. To the best of our knowledge, this is the first catalytic ring-closure reaction arising from dihaloalkanes under chemical reductive conditions.

This work features first asymmetric Ni-catalyzed reductive coupling of allylic carbonates with aldehydes, which may proceed via allyl-Ni intermediates although Zn was used as the terminal reductant. Moderate to excellent enantiomeric excess was obtained with excellent functional group tolerance.

The use of bis(pinacolato)diboron as the terminal reductant allows the efficient Ni-catalyzed coupling of unactivated secondary and primary alkyl halides, generating the C(sp3)–C(sp3) coupling products in good yields. The mild catalytic conditions display excellent functional group tolerance, and good chemoselectivities which require only 1.5 equiv. of primary bromides for the coupling with secondary bromides. Preliminary mechanistic studies suggest that an in situ organoborane/Suzuki process is not likely. It was identified that the base and ligand have more profound impact on selecting this reductive coupling pathway. The good chemoselectivity appears to be evoked by the formation of Ni–Bpin catalytic intermediates, which demands matched sizes and reactivities of the alkyl halide coupling partners for optimal coupling efficiency.

This paper highlights Ni-catalyzed allylation of electron-rich aryl bromides with a variety of substituted allylic carbonates using zinc as the terminal reductant, affording E-alkenes regioselectively in good to excellent yields by the addition of aryl to the less hindered allylic carbon. The electron-deficient aryl bromides and chlorides are also highly efficient coupling partners.

Ni-catalyzed ketone formation through mild reductive coupling of a diverse set of unactivated alkyl bromides and iodides with particularly aryl acid anhydrides was successfully developed using zinc as the terminal reductant. These conditions also allow direct coupling of alkyl iodides with aryl acids in the presence of Boc2O and MgCl2.

A room-temperature Ni-catalyzed reductive method for the coupling of aryl bromides with secondary alkyl bromides has been developed, providing C(sp2)–C(sp3) products in good to excellent yields. Slight modification of this protocol allows efficient coupling of activated aryl chlorides with cyclohexyl bromide and aryl bromides with allylic acetate.

The present work highlights unprecedented Ni-catalyzed reductive coupling of unactivated alkyl iodides with aryl acid chlorides to efficiently generate alkyl aryl ketones under mild conditions.

The formation of C–C bonds directly by catalytic reductive cross-coupling of two different electrophiles represents one of the practical synthetic protocols that differs from the conventional nucleophile/electrophile coupling methods. Particularly the reductive coupling of alkyl electrophiles with other electrophiles is still a challenge. This report summarizes the advances in the formation of C(sp3)–C(sp3) bonds between two alkyl electrophiles, with emphasis on the control of chemoselectivity that is exceedingly challenging to achieve due to similar structures and reactivities of two unactivated alkyl halides. The coupling of alkyl halides with aryl or acyl electrophiles was also discussed based on the chemical approach developed by our group, followed by a brief overview of the reactions of tertiary alkyl halides. In the end, a brief overview of the challenges in this exciting field was illustrated. Whereas the reaction mechanisms generating alkyl–alkyl products are proposed to involve reactions of Ni(I) species with alkyl halides to generate Ralkyl–Ni(III)–Ralkyl intermediates through a radical/Ni cage-rebound process, the obtained evidence seemingly supports that the radical chain mechanism governs the acylation and arylation of alkyl halides. The latter features a cage-escaped alkyl radical.

Correction for ‘Nickel-catalyzed reductive coupling of alkyl halides with other electrophiles: concept and mechanistic considerations’ by Jun Gu et al., Org. Chem. Front., 2015, 2, 1411–1421.

The present work disclosed a considerably improved method for the construction of alkyl–aryl ketones by the direct coupling of unactivated alkyl bromides with 1.5 equiv. of acids. In addition, the synthesis of aroyl C-glycosides was first achieved by the reductive coupling of 1-glycosyl bromides with acid derivatives, which may otherwise require multi-step synthesis.

This work features first asymmetric Ni-catalyzed reductive coupling of allylic carbonates with aldehydes, which may proceed via allyl-Ni intermediates although Zn was used as the terminal reductant. Moderate to excellent enantiomeric excess was obtained with excellent functional group tolerance.

Ni-catalyzed ketone formation through mild reductive coupling of a diverse set of unactivated alkyl bromides and iodides with particularly aryl acid anhydrides was successfully developed using zinc as the terminal reductant. These conditions also allow direct coupling of alkyl iodides with aryl acids in the presence of Boc2O and MgCl2.

The use of bis(pinacolato)diboron as the terminal reductant allows the efficient Ni-catalyzed coupling of unactivated secondary and primary alkyl halides, generating the C(sp3)–C(sp3) coupling products in good yields. The mild catalytic conditions display excellent functional group tolerance, and good chemoselectivities which require only 1.5 equiv. of primary bromides for the coupling with secondary bromides. Preliminary mechanistic studies suggest that an in situ organoborane/Suzuki process is not likely. It was identified that the base and ligand have more profound impact on selecting this reductive coupling pathway. The good chemoselectivity appears to be evoked by the formation of Ni–Bpin catalytic intermediates, which demands matched sizes and reactivities of the alkyl halide coupling partners for optimal coupling efficiency.

This paper highlights Ni-catalyzed reductive trapping of secondary and tertiary alkyl radicals with both electron-rich and electron-deficient aryl isocyanides using zinc as the terminal reductant, affording 6-alkylated phenanthridine in good yields. The employment of carbene ligands necessitates the alkyl radical process, and represents the first utility in the Ni-catalyzed reductive conditions for the generation of unactivated alkyl radicals from the halide precursors.

This paper highlights Ni-catalyzed allylation of electron-rich aryl bromides with a variety of substituted allylic carbonates using zinc as the terminal reductant, affording E-alkenes regioselectively in good to excellent yields by the addition of aryl to the less hindered allylic carbon. The electron-deficient aryl bromides and chlorides are also highly efficient coupling partners.