C-O Activation by a Rhodium Bis(N-Heterocyclic Carbene) Catalyst: Aryl Carbamates as Arylating Reagents in Directed C-H Arylation.

Despite recent progress in the catalytic transformation of inert phenol derivatives as alternatives to aryl halides and triflates, attempts at the cross-coupling of inert phenol derivatives with the C-H bonds of arenes have met with limited success. Herein, we report the rhodium-catalyzed cross-coupling of aryl carbamates with arenes bearing a convertible directing group. The key to success is the use of an in situ generated rhodium bis(N-heterocyclic carbene) species as the catalyst, which can promote activation of the inert C(sp2 )-O bond in aryl carbamates.

Cobalt-catalyzed chelation assisted C-H allylation of aromatic amides with unactivated olefins.

The cobalt-catalyzed chelation assisted ortho C-H allylation of aromatic amides with unactivated aliphatic alkenes is reported. The reaction proceeds in air under mild reaction conditions, providing allylated products in good to excellent yields with high E-selectivities. This operationally simple method shows a high functional group tolerance.

Chelation-Assisted Nickel-Catalyzed Oxidative Annulation via Double C-H Activation/Alkyne Insertion Reaction.

A nickel/NHC system for regioselective oxidative annulation by double C-H bond activation and concomitant alkyne insertion is described. The catalytic reaction requires a bidentate directing group, such as an 8-aminoquinoline, embedded in the substrate. Various 5,6,7,8-tetrasubstituted-N-(quinolin-8-yl)-1-naphthamides can be prepared as well as phenanthrene and benzo[h]quinoline amide derivatives. Diarylalkynes, dialkylalkynes, and arylalkylalkynes can be used in the system. A Ni(0)/Ni(II) catalytic cycle is proposed as the main catalytic cycle. The alkyne plays a double role as a two-component coupling partner and as a hydrogen acceptor.

Scalable C-H Oxidation with Copper: Synthesis of Polyoxypregnanes.

Steroids bearing C12 oxidations are widespread in nature, yet only one preparative chemical method addresses this challenge in a low-yielding and not fully understood fashion: Schönecker's Cu-mediated oxidation. This work shines new light onto this powerful C-H oxidation method through mechanistic investigation, optimization, and wider application. Culminating in a scalable, rapid, high-yielding, and operationally simple protocol, this procedure is applied to the first synthesis of several parent polyoxypregnane natural products, representing a gateway to over 100 family members.

Ni(II)-catalyzed oxidative coupling between C(sp(2))-H in benzamides and C(sp(3))-H in toluene derivatives.

Oxidative coupling between C(sp(2))-H bonds and C(sp(3))-H bonds is achieved by the Ni(II)-catalyzed reaction of benzamides containing an 8-aminoquinoline moiety as the directing group with toluene derivatives in the presence of heptafluoroisopropyl iodide as the oxidant. The method has a broad scope and shows high functional group compatibility. Toluene derivatives can be used as the coupling partner in an unreactive solvent.

Nickel(II)-catalyzed direct arylation of C-H bonds in aromatic amides containing an 8-aminoquinoline moiety as a directing group.

Arylation via the cleavage of the ortho C-H bonds by a nickel-catalyzed reaction of aromatic amides containing an 8-aminoquinoline moiety with aryl iodides is reported. The reaction shows a high functional group compatibility. The reaction proceeds in a highly selective manner at the less hindered C-H bonds in the reaction of meta-substituted aromatic amides, irrespective of the electronic nature of the substituents. Electron-withdrawing groups on the aromatic amides facilitate the reaction. Various mechanistic experiments, such as deuterium labeling experiments, Hammett studies, competition experiments, and radical trap experiments, have been made for better understanding the reaction mechanism. It is found that the cleavage of C-H bonds is reversible on the basis of the deuterium labeling experiments. Both Ni(II) and Ni(0) show a high catalytic activity, but the results of mechanistic experiments suggest that a Ni(0)/Ni(II) catalytic cycle is not involved.

Direct arylation of C(sp3)-H bonds in aliphatic amides with diaryliodonium salts in the presence of a nickel catalyst.

The Ni(II)-catalyzed direct arylation of C(sp(3))-H (methyl and methylene) bonds in aliphatic amides containing an 8-aminoquinoline moiety as the directing group with diaryliodonium salts as coupling electrophiles is described. A wide variety of functional groups are tolerated in the reaction. The reaction represents the first example of the Ni-catalyzed direct arylation of C(sp(3))-H bonds with diaryliodonium salts.

Nickel-catalyzed direct arylation of C(sp3)-H bonds in aliphatic amides via bidentate-chelation assistance.

The Ni-catalyzed, direct arylation of C(sp(3))-H (methyl and methylene) bonds in aliphatic amides containing an 8-aminoquinoline moiety as a bidentate directing group with aryl halides is described. Deuterium-labeling experiments indicate that the C-H bond cleavage step is fast and reversible. Various nickel complexes including both Ni(II) and Ni(0) show a high catalytic activity. The results of a series of mechanistic experiments indicate that the catalytic reaction does not proceed through a Ni(0)/Ni(II) catalytic cycle, but probably through a Ni(II)/Ni(IV) catalytic cycle.

Nickel-catalyzed direct alkylation of C-H bonds in benzamides and acrylamides with functionalized alkyl halides via bidentate-chelation assistance.

The alkylation of the ortho C-H bonds in benzamides and acrylamides containing an 8-aminoquinoline moiety as a bidentate directing group with unactivated alkyl halides using nickel complexes as catalysts is described. The reaction shows high functional group compatibility. In reactions of meta-substituted aromatic amides, the reaction proceeds in a highly selective manner at the less hindered C-H bond.

Nickel-catalyzed chelation-assisted transformations involving ortho C-H bond activation: regioselective oxidative cycloaddition of aromatic amides to alkynes.

Although the pioneering example of ortho metalation involving cleavage of C-H bonds was achieved using a nickel complex (Kleiman, J. P.; Dubeck, M. J. Am. Chem. Soc. 1963, 85, 1544), no examples of catalysis using nickel complexes have been reported. In this work, the Ni-catalyzed transformation of ortho C-H bonds utilizing chelation assistance, such as oxidative cycloaddition of aromatic amides with alkynes, has been achieved.