Rhodium‐Catalyzed Alkylation of C−H Bonds in Aromatic Amides with Non‐activated 1‐Alkenes: The Possible Generation of Carbene Intermediates from Alkenes

Abstract

The alkylation of C−H bonds (hydroarylation) in aromatic amides with non‐activated 1‐alkenes using a rhodium catalyst and assisted by an 8‐aminoquinoline directing group is reported. The addition of a carboxylic acid is crucial for the success of this reaction. The results of deuterium‐labeling experiments indicate that one of deuterium atoms in the alkene is missing, suggesting that the reaction does not proceed through the commonly accepted mechanism for C−H alkylation reactions. Instead the reaction is proposed to proceed through a carbene mechanism. The carbene mechanism is also supported by preliminary DFT calculations.

Mechanistic Interrogation of Alkyne Hydroarylations Catalyzed by Highly Reduced, Single-Component Cobalt Complexes

“…Chelation-assisted C–H activations allow selective functionalization of unreactive C–H bonds, thereby accessing atom-economical, late-stage molecular modifications without the installation of wasteful cross-coupling partners. − In this context, hydroarylation has emerged as an attractive method to form C–C bonds via the addition of activated aryl C–H bonds across olefins or alkynes. In the past two decades, catalyst development for such reactions has been aided by mechanistic investigations. ,− The first report of olefin hydroarylation from the Murai group , described RuH 2 (CO)­(PPh 3 ) 3 as the pre-catalyst, and more recent advances in hydroarylations are based on pre-catalysts bearing a metal center with a square-planar d 8 or octahedral d 6 configuration (e.g., Rh, − Ir, − Pd, and Pt − ). Significantly, mechanistic studies with these second- and third-row transition metal catalysts implicate a rate-limiting C–H addition. − By comparison, far fewer first-row transition metal hydroarylation catalysts have been identified, despite recent efforts to exploit the high abundance and low costs of Fe, Co, , and Ni. − Future catalyst designs should rely on mechanistic information that is largely non-existent, and notably, first-row metals often engage in mechanisms that are distinctly different from those of heavier transition metals. ,, …”

Transition-metal-catalyzed C–H bond alkylation using olefins: recent advances and mechanistic aspects

“…The overall reaction was proven to have a versatile substrate scope. Subsequently, the authors expanded the substrate scope by performing the C–H alkylation of aromatic amides with a wide range of maleimides 15f , 66 non-activated 1-alkene 15h , 67 and N -vinylphthalimide 15j . 68 In the case of non-activated 1-alkene, the presence of carboxylic acid in the medium is one of the mandatory conditions for efficient transformation.…”

“…However, in the case of electron-withdrawing substituents, the amount of branched selective product increased. 67 Linear selective alkylation proceeds via generation of an Rh-carbene intermediate. In contrast, branched selective alkylation follows the common type I mechanistic pathway ( cf.…”

A facile method for Rh-catalyzed decarbonylative ortho-C–H alkylation of (hetero)arenes with alkyl carboxylic acids

“…These well-established limitations have encouraged the development of alternative metal-catalyzed directed alkylation of (hetero)arenes C–H bonds, 5 one of the most accurate and effective tools, therein, highly regioselectivity mostly relies on the use of a directing group by allowing the metal center proximally close to the target C–H bonds in the starting (hetero)arenes. To date, this directed C–H alkylation of (hetero)arenes undergoes with diverse alkylating agents within which alkenes 5 j , l , p and alkyl halides 5 c are mostly used reagents.…”

“…Encouraged by Daugulis's pioneering work and others' previous studies, 5 herein we select 8-aminoquinoline (AQ), an excellent N , N -bidentate directing group in catalytic functionalization of C–H bonds, 8,9 as the installed moiety on the starting (hetero)arenes, and expect to develop a general method for Rh-catalyzed decarbonylative C–H alkylation of (hetero)arenes with in situ generated alkyl carboxylic acid anhydrides ( Scheme 1b ).…”