Recent Advances in Rare‐Earth Metal‐Catalyzed C−H Functionalization Reactions

Abstract

There has been a persistent impetus for the development of versatile C−H functionalization reactions, which represents a powerful approach to a wide variety of valuable chemical compounds. Transition metal catalyzed C−H functionalization has attracted intense interest and witnessed considerable advances in this field owing to its outstanding regioselectivity and atom‐economy. In recent years, rare‐earth (RE) metal‐based catalysts have been successfully employed in this flourished area, demonstrating unique selectivity and complementary reactivity with respect to late‐transition metal‐catalyzed C−H functionalization. The development of rare‐earth metal‐catalyzed C−H functionalization by taking the advantage of these characteristic properties is of great importance and interest. Herein, a panorama of rare‐earth metal‐catalyzed C−H functionalization during the last decade is presented.

Substrate Facilitating Roles in Rare-Earth-Catalyzed C–H Alkenylation of Pyridines with Allenes: Mechanism and Origins of Regio- and Stereoselectivity

“…As mentioned above, cationic rare-earth catalysts have achieved C–H functionalization of various heteroatom-containing substrates (Scheme ). − Therefore, as an essential step in reaction transformations, the C–H activation event is of particular interest and importance. DFT results show that although the allene insertion occurs via a pyridine-coordinated mechanism, the initial C­(sp 2 )–H activation for the generation of catalytically active species and the final protonation [C­(sp 2 )–H activation] steps occur through a pyridine-free mechanism.…”

“…As an emerging field, cationic rare-earth (scandium, yttrium, and lanthanides) alkyl complexes have been found to be a powerful platform for the C–H addition of various heteroatom-containing substrates (such as pyridines, quinolines, aldimines, imidazoles, sulfides, anisoles, anilines, amines, and ferrocenes) to alkenes and alkynes in the past decade (Scheme ). Notably, these reactions often feature high regio-, stereo-, and chemo-selectivity, which are often superior or complementary to transition-metal catalysts due to their unique chemical reactivities . Cationic rare-earth catalysis has opened new horizons for C–H functionalization; however, the lack of atomic-level understandings of reaction mechanisms and origins of selectivities makes the rational design of new reactions challenging.…”

“…As an example, recently, we have found that the regioselectivity in yttrium-catalyzed C–H functionalization of quinolines using alkenes could be changed by coordinating a quinoline substrate in the alkene insertion step, which obviously indicates that the coordination effect of the substrate (as a ligand) is significant during the catalytic cycle . However, the previously reported/proposed mechanisms based on experimental or computational results almost ignored the potential coordination effect of heteroatom-containing substrates, which sometimes makes us confused about the versatile reactivities in rare-earth catalytic systems . Whether and how an extra heteroatom-containing substrate as a ligand influences the C–H activation and CC/CC bond insertion processes at the rare-earth metal center remains highly underestimated.…”

“…Therefore, it has received tremendous interest in organic synthesis . As an emerging field, cationic rare-earth (scandium, yttrium, and lanthanides) alkyl complexes have been found to be a powerful platform for the C–H addition of various heteroatom-containing substrates (such as pyridines, quinolines, aldimines, imidazoles, sulfides, anisoles, anilines, amines, and ferrocenes) to alkenes and alkynes in the past decade (Scheme ). Notably, these reactions often feature high regio-, stereo-, and chemo-selectivity, which are often superior or complementary to transition-metal catalysts due to their unique chemical reactivities .…”

Accessing unnatural α-amino acids with tetrasubstituted stereogenic centersviacatalytic enantioselective reactions of ketimine-type α-iminoesters/α-iminoamides

“…In 2020, Xu and co-workers reported the use of sixmembered 1,2,6-thiadiazine-1,1-dioxide-type cyclic sulfonyl aiminoesters 154 as electrophiles in palladium-catalyzed enantioselective arylation chemistry (Scheme 62). 98 This reaction proceeds efficiently in the presence of chiral phosphinooxazoline-ligated palladium complex 156 to afford chiral ATAAs 155 with high enantioselectivities. Furthermore, ATAA 155 is easily converted into chiral g-lactam 157 bearing atetrasubstituted a-amino acid moiety, which is analogs of a TNF-a convertase enzyme (TACE) inhibitor and an antiinflammatory agent, without loss of enantiopurity.…”