Ligand‐Promoted Rhodium(III)‐Catalyzed ortho‐C−H Amination with Free Amines

Abstract

Ligand development for rhodium(III)-catalyzed C-H activation reactions has largely been limited to cyclopentadienyl (Cp) based scaffolds. 2-Methylquinoline has now been identified as a feasible ligand that can coordinate to the metal center of Cp*RhCl to accelerate the cleavage of the C-H bond of N-pentafluorophenylbenzamides, providing a new structural lead for ligand design. The compatibility of this reaction with secondary free amines and anilines also overcomes the limitations of palladium(II)-catalyzed C-H amination reactions.

Distal Weak Coordination of Acetamides in Ruthenium(II)‐Catalyzed C−H Activation Processes

“…[2] As aconsequence,there is acontinued high demand for general strategies that provide access to substituted arylacetamides in as ustainable fashion.In recent years,catalyzed C À Hactivation has emerged as at ransformative tool for molecular syntheses. [3] While direct functionalizations of simple benzamides have thus been accomplished, [4] CÀHa ctivations of distal weakly coordinating acetamides via unfavorable six-membered metallacycles continue to be scarce,w ith pioneering contributions in palladium catalysis by Yu,M aiti, and Dong, among others. [5,6] Despite undisputable recent progress by versatile, less expensive [7a] ruthenium catalysis, [7] C À Hf unctionalizations of challenging arylacetamides have thus far remained elusive,which is largely because of the tautomerizable nature of the distal O-coordinating acetamides.Within our program on cost-effective C À Ha ctivation, [8] we have now developed uniquely effective oxidative C À H alkenylations [9] of weakly coordinating acetamides,o nw hich we report herein.…”

“…In recent years,catalyzed C À Hactivation has emerged as at ransformative tool for molecular syntheses. [3] While direct functionalizations of simple benzamides have thus been accomplished, [4] CÀHa ctivations of distal weakly coordinating acetamides via unfavorable six-membered metallacycles continue to be scarce,w ith pioneering contributions in palladium catalysis by Yu,M aiti, and Dong, among others. [5,6] Despite undisputable recent progress by versatile, less expensive [7a] ruthenium catalysis, [7] C À Hf unctionalizations of challenging arylacetamides have thus far remained elusive,which is largely because of the tautomerizable nature of the distal O-coordinating acetamides.…”

Synthesis of Diverse Functionalized Quinoxalines by Oxidative Tandem Dual C−H Amination of Tetrahydroquinoxalines with Amines

“…In particular, in some cases, the use of strong oxidants can easily result in poor substrate and functional group compatibility as well as pollution issues. From the viewpoint of sustainability, the development of direct C−H amination protocols with easily available agents, preferably with free amines as the aminating agents and naturally abundant catalysts and oxidants, still remains a highly important goal…”

Ligand‐Promoted RhIII‐Catalyzed Thiolation of Benzamides with a Broad Disulfide Scope

“…[13] In 2016, Liusg roup developed aN i-catalyzed C À H activation/thiolation reaction enabled by an amino acid auxiliary as ab identate directing group. [14] Inspired by this work, and encouraged by our previous work focusing on the ligand-promoted Rh III -catalyzed olefination, [15] arylation, [16] and amination [17] of N-pentafluorophenyl benzamides,w e intended to apply this weakly coordinating monodentate directing group to Rh III -catalyzed ortho-CÀHt hiolation reaction with the assistance of amino acid derivatives.W e hypothesized that coordination of an amino acid ligand to the rhodium center could suppress the catalyst deactivation caused by strong sulfur coordination. With this consideration in mind, we first investigated 18 ligands in the Rh III -catalyzed coupling of amide 1aa and phenyl disulfide 2a,using 5mol % [RhCp*Cl 2 ] 2 ,2 0mol %l igand, and 1.5 equiv of Ag 2 Oi n dichloromethane (DCM) at 70 8 8Cf or 12 h ( Table 1).…”

“…In contrast, Boc-leucine afforded exclusively the dithiolated product when the temperature was increased to 90 8 8C( entry 11). When the Boc group was absent, tert-leucine gave adramatically decrease of yield into 10 %( entry 18), thus suggesting that an electronwithdrawing N-protecting group is critical for supporting catalyst turnover by suppressing catalyst poisoning.F urthermore,amino acids with hydrophilic side chain are unfavorable in the reaction (entries [15][16][17]. Control experiment showed that only 5%of monothiolated product was observed without ligand, thus indicating the important roles of the amino acid ligand in stabilizing the catalytic center and promoting C À H activation (entry 19).…”